PHOTOREACTIONS OF PARTIALLY BLINDED WHIP-TAIL

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P H O T O R E A C T IO N S O F P A R T I A L L Y B L I N D E D W H I P - T A IL

S C O R P I O N S .

BY BRADLEY M. PATTEN.

(From the Laboratory of Histology and Embryology, School of Medicine, WesternReserve University, Cleveland.)

(Received for publication , Decem ber 11, 1918.)

INTI~ODUCTIO!~.

The experiments deal t with in this paper were devised to ascertain

(1) the relat ive effect iveness as photore ceptors of the w hip-tai l scor-

pion's media n eyes, lateral eye groups, and cutaneo us sensi tive areas,

and (2) the e ffec t on or ientat ion produced by symmetr ica l and b y

asymmetr ica l inte rfe rence wi th the photorecept ive mechanism.

Mos t of the animals fami l ia r in the l i t e ra ture on photot ropism have

l ight-sensit ive mecha nisms which consist of a single pair of receptors,

or mechanisms in which one of the receptors overshadows the others

in effect iveness. The whip-tai l scorpion has three pairs of photo re-

ceptors, each of which, act ing alone, is capable of bringing abou t orien-

tation . It offers, therefore, un usu ally varie d possibilities for experi-

men ts a l te ring the normal , symmetr ica l condi t ion of the photorecep-

t ive mechanism.As a basis for work ing on part ial ly bl ind ed scorpions, the responses

of normal animals were quant i t a t ive ly de te rmined. The resul ts of

this prel imina ry work h ave already been published (1), but certain of

the more impo rtant point s may be s umm arized here. The species of

whip-tai l used (Mastigoproctus giganteus Lucas) was found to be

negatively phototrop ic, and very consistent in i ts precision of orienta-

t ion. The m ethod of measur ing the normal reac t ions and the ex-

per imenta l condi t ions under which the measurements were carr ied out ,

were chosen with a view to making even sl ight changes in react ion

clearly recognizable. Responses to known intensi t ies of i l lumina t ion

435

The Journal of General Physiology

Published March 20, 1919



436 PHOTOP,~EACTIONS OP VC-HIP-TAIL SC OR PI ON S

were recorded in terms of def lection from an init ial direction of loco-

mot ion. Def lec t ion ampl i tudes were measu red in degrees by record-ing the animal ' s point of emergence f rom a gradua ted c i rc le . By

mak ing th e diam eter of the c i rcle r e la t ive ly smal l (50 cm.) , the ra te of

a t ta ining or ienta t ion, as wel l as the acc uracy of or ienta t ion, was m ade

measureable .

T he a c c ur a c y of o r ie n t a ti on e xh ib i t e d by nor ma l a n ima l s w he n

placed be tween equa l , opposed beams of l ight , was measured as the

r e a c ti on w hic h w ou ld be mos t r e a d il y d i s t u r bed by a ny a symm e t r i c a l

in te r fe rence wi th the recept ive mechanism. Def lec t ion ampl i tudes of

animals subjec ted to ante r ior and to la te ra l i l lumina t ion were meas-

ured as be ing the reac t ions which w ould be most extens ive ly changed by

sym metr ica l e l imina t ions of r eceptors .

The exper iments on par t ia l ly bl inded animals repor ted be low were

car r ied out wi th the same intens i ty of il lumina t ion, and the sam e

meth od of handl ing used on normal animals . Change f rom the nor -

mal reac t ion fol lowing the e l imina t ion of a photoreceptor can, there -

fore, be take n as a meas urable ind ex of the effectiveness of the recep tor

preven ted f rom func tioning. A se r ies of exper iments in which a l l

possible cases of el imination are carr ied out wil l show at the same

t ime the re la t ive e f fec t iveness of th e di f fe rent mem bers of the recept ive

sys tem, and the e f fec t on or ienta t ion produced by symm etr ica l and

by asym metr ica l in te r fe rence wi th the photoreceptors .

Apparatus.

The appara tus used in these exper iments was the same as tha t used

in measur ing the reac t ions of norm al animals . I t i s shown in F ig. 1 .

Dete rmina t ions of the i l lumina t ion de l ivered by the l ights were

mad e wi th a Bunsen photom eter . Each f ixed l ight gave an i l lumina-

t ion of 120 candle mete rs at the cen ter of the observa tion circle. Th e

intens i ty of the th i rd l ight could be var ied by moving i t to d i f fe rent

posit ions along the axis. Th e whole appa ratus was located in a dark

room and in order to reduce re f lec ted l ight to a m inimum , a ll pa r t s of

i t except the scales were painted f iat black.




B R A D L E Y ~ . P A T T E N " 437

Methods.

T h e g e n e r a l e x t e r n a l a n a t o m y o f t h e w h i p - t a i l s c o r p i o n a n d t h e

m o r e i m p o r t a n t p o i n t s c o n c e r ni n g it s e x p e r i m e n t al h a n d l i n g h a v e

b e e n t a k e n u p in a p r e l i m i n a r y p a p e r ( 1 ) . F o r a d e t a i l e d m o r p h o -

l o g ic a l c o n s i d e r a t i o n o f t h e g r o u p t o w h i c h Mastigoproctus giganteus

I),,30 LO rO I , 0 ZO

~0 30

6 60

;? i

+r; . . . . ~ .o + _ , , . . . . . ' ~ ~-+~.;++:/-~:+.:+L+++

Y,

®S

FIG. 1. Plan of appara tus. Abou t O as a center a circle 50 cm. in diame ter

was described and gradu ated in degrees. This is term ed the "observ ation circle".

The axis ppt is constructed parallel to the edge of the table and the axis yyPper-

pendicular to pp'. On the axis yyt two 15 watt Mazda lamps, A and B, were setup, each distant 35 cm. from the center of the circle. On the axis pp' a similar

lamp was mounte d on a mova ble frame, C. Affixed at right angles to the base of

the frame, C, was a scale, V, reading as a vern ier against the scale, S, at the edge

of the table. Light-p roof cases, s,s,s, enclosed each light except for diaphragms

3 X 3 cm. so placed that the beams of light transmitted each centered at O.

b e l o n g s r e f e r e n c e s h o u l d b e m a d e t o B 6 r n e r ( 2 ). T h e s k e t c h o f Masti-

goproctus reproduced in F ig . 2 wi l l s e rve to g ive the loca t ion of the

p h o t o r e c e p t o r s c o n s i d e r e d i n t h i s p a p e r .

A s h a s a l r e a d y b e e n s ta t e d , t h e m e t h o d m a p p e d o u t f o r se c u r in g

d a t a o n t h e e f f e c t i v e n e ss o f t h e v a r i o u s p h o t o r e c e p t o r s c o n s i s t e d i n

c o m p a r i n g w i t h t h e r e a c t i o n s o f n o r m a l a n i m a ls , t h e r e a c t i o n s o f an i -




438 PHOTOI~EACTIONS OF WHIP-TAIL SCORPIONS

r e a l s i n w h i c h p a r t s o f t h e l i g h t - s e n s i t i v e s y s t e m h a d b e e n p r e v e n t e d

f r o m f u n c t i o n i n g . V a r i o u s m e a n s o f e li m i n a t i n g t h e l a te r a l a n dm e d i a n e y e s w e re c o n s i d e re d . T h e r e s e e m e d n o j u s t if i c a ti o n , i n t h e

-%

t !!I

I

e

-I

Ce r~ t Lmete r s .

FIG. 2. Mastigoproctus giganteus Luca s. 1, chelicera~; 2, pedipalps; 3, modified

anterior legs which serve as feelers; 4, 5, 6, walking legs; me, median eyes; le, lat-

eral eye group consisting of three eyelets clustered v ery close together in the form

of a miniature triangle.

c a s e of a n a n i m a l i n w h i c h t h e e y e s c o u ld b e e f f e c t i v e l y c o v e r e d , f o r

s u c h v i o l e n t m e t h o d s a s e x t i r p a t i o n o r c a u t e r i z a t i o n w i t h t h e i r p o s -

s ib le d i s turb ing a f t e r -e f fec t s . Th e fo l lowing two me tho ds of cover in g




BI~ADLEY M. PATTEI~ 43 9

the eyes were bo th found to be sa t i s fac to ry and one o r the o ther was

used, wi thout preference, in the series of experiments .1 . Asphal tum varn i sh was app l i ed wi th a camel ' s ha i r penc i l t o

the surface of the eye and al lowed to dry unt i l s t icky. A cap of tin-

fo i l cu t t o f i t over the eye was then se t i n the vamish and a l lowed to

dry in hard . F ina l ly ano ther coa t of aspha l tum w as pu t over the

cap, especial care being used to seal the edges t ight ly .

2 . Rubber adhes ive t ape was g iven two coa t s o f aspha l tum varn i sh

on the fab r i c su r face . Wh en the second coa t had d r i ed, t he t ape was

cut in to caps of the desi red s ize, which were pressed f i rmly over the

eyes . The caps were then sea led on wi th aspha l tum varn i sh and

al lowed to dry.

Subsequen t microscop ica l examina t ion o f c l eaned exoske le tons o f

an imals in which the ey es had been ca pped in these ways gave noindicat ion of l ight leakage. Furth erm ore, ei ther type of covering

cou ld be removed , l eav ing the eye un in ju red fo r con tro l exper imen t s .

The f i r st an imals hand led a f t e r the capp ing o f bo th med ian eyes

and both lateral eye groups showed s t i l l a wel l defined sensi t iveness to

l ight. Af ter careful rechecking of the work for poss ible l ight leakage

around the caps showed tha t t he eyes were e f fec t ive ly covered , a

sys t emat i c search was begun fo r cu taneous pho tosens i t ive a reas}

Animals were placed under vert ical i l luminat ion of jus t suff icient in-

t ens i ty to ma ke the i r ou t l ines d i scern ib le and searched wi th a po in t o f

in t ense l igh t ob ta ined by p lac ing a tungs ten f l ash l igh t bu lb in p l ace

of the ocu lar o f a compoun d microscope and converging the rays th rough

the ob jec t ive (3) . As migh t be expec ted , the a reas o f the body cov-

ered by thick, heavi ly pigmented chi t in were insensi t ive to l ight .

This narrowed the search to two local i t ies : the "feel ing legs" (see

Fig . 2 ) wh ich had a l ready been demons t ra t ed to be sens i t ive to touch

1 The possibility that blinded scorpions mig ht be reacting to the heat of the

light was tested in the followingway. Anim alswere illuminated from one side bylight of 120 candle meters. On the opposite side, 20 cm. distant from the scor-pion, was placed a flatiron emanating heat rays plainly discernible to the back of

the hand. The light drove both normal animals and animals with their m edianand lateral eyes capped toward th e iron until the y burned their feelers on it.In spite of their crudeness these experiments served to rule ou t the possibility ofa heat reaction playing any part under the conditions of these experiments.




440 PHOTOREACTIONS OF WHIP-TAIL SCORPIONS

and to chemicals, and the areas of extremely thin and unpigmented

chitin around the articulations of the appendages with the sides ofthe cephalothorax. Careful searching of the feelers with the light

spot failed to elicit any reaction from the animal or movement of

the feelers. Furthermore when the feelers were cut off several

animals, some of which were otherwise normal and some of which

had both median and lateral eyes capped, the characteristic orienta-

tion to light was in neither case affected.

Attention was then turned to the areas of thin chitin at the sides

of the cephalothorax. Searching these areas with the light spot

caused the animals to tur n away from the illuminated side. The

same areas were then rendered opaque by painting with asphaltum

varnish." Animals with one side of the cephalothorax blackened,

when subjected to bilaterally balanced illumination, showed a verymark ed deflection toward the blackened side. This deflection was

not attributable to mechanical interference with locomotion due to

the presence of the varnish, for when stimulated mechanically, the

animals did not move in curves. In anothe r series of cases, scorpions

with all eyes capped and both sides of the cephalothorax blackened

were found to be insensitive to light. Methylene blue preparations

of the integument in this region made subsequently showed abundant

ganglion cells and nerve endings.

These observations indicated that the analysis of the receptive

mechanism must deal with three elements: the median eyes, the lat-

eral eye groups, and the photosensitive areas at the sides of the

cephalothorax where the legs articulate with the body. Wit h ef-

fective methods of preventing any receptor or group of receptors from

functioning, the work resolved itself into series of measurements in

which all possible combinations of interference with the photorecep-

tots should be covered.

2 The results of this treatment were at first somewhat unsatisfactory becauseof the mucus thrown out when the areas in question were irri tatedby the varnish.It was possible, however, by repeated paintings to get a nearly unbroken coat ofvarnish to adhere. Animals reated in this way had to be used in the desiredexperiments before the varnish had dried long enough to become brittle.




BI~ADLEY M. PATTEN 44 1

Reaction Measurements.

In a l l the tes t s wi th par t ia l ly bl inded animals , grea t ca re was used

to reproduce the exper imenta l condi t ions under which the cor re -

spond ing t e st s on nor ma l an ima ls ha d be e n ma de . T he m e thod o f

ha nd l ing t he a n ima l s a nd t he me thods o f me a sur ing a nd t a bu l a t i ng

the reac t ions were the same as those descr ibed for normal animals (1).

The de ta i l s have , there fore , been omi t ted and the da ta presented only

in the form of tabula r and graphic summar ies .

For convenience in presenta t ion a nd considera t ion, the reac t ion

mea surem ents have been col lec ted in three groups: (1) The reac t ions

• to ba lanced opposed i l lumina t ion of animals subjec ted to asy mm etr i -

ca l in te r fe rence wi th the pho~orecept ive mechanism . (2) The reac-

t ions to ba lanced opposed i l lumina t ion of animals subjec ted to sym-

metr ica l in te r fe rence wi th the photorecep t ive mech anism. (3) The

reac t ions to la te ra l and to ante r ior i l lumina t ion of animals subjec ted

to sym metr ica l in te r fe rence wi th the pho torecept ive mechan ism.

R~actions to Balanced Opposed Illumin ation of An ima ls Subjected to

Asymm etrical Interference with the Photoreceptive Mechanism.

In a l l the e xper iments on asy mm etr ica l in te r fe rence , the blackening

was car r ied out on the r ight s ide in one-ha l f of the animals , and on

the le f t s ide in the o ther ha l f of the individua ls used. Tables I and

I I show the result s of meas ureme nts mad e on animals wi th one la t-

eral eye gro up capped, and on animals w ith one side of~ the cephalo-

thorax blackened. These tables a re given in de ta il pa r t ly as i l lus-t ra t ions of the method of handl ing the measurements , but espec ia l ly

to show the consis tency and the range of individua l var iabi l i ty en-

counte red in typica l se ries of measuremen ts . Qu al i ta t iv e ly there can

be no doubt as to the s igni ficance of the react ions . The ap proxim ate

consis tency of the individua l r eac t ions would indica te tha t averages

obta ined f rom the ten t r ia l s of an animal express wi th reasonable

quant i ta t ive accuracy the va lue of the reac t ion.

In the case of the other se r ies of measu remen ts de tai led tables have

be e n omi t t e d a nd on ly the sum ma r y o f t he r esu l ts p r e sen t e d . T a b l e

I I I summa r i z es t he me a sur e m e n t s ma de unde r ba l a nc e d i l lumina t ion ,

on animals subjec ted to asym metr ica l in te r fe rence wi th the photo-

receptors.




T A B L E I .

Reactions to Balanced Il lumination of Animals with Lateral Eye Group on One

Side of I-lead Covered. Mea surem ents Recorded in Degrees of Defleclion

fro m Ini tial P ath of Locomotion Perpe ndicula r to Lin e Connecting

Two Sources of Light.

No. oftrial.

to right.

degrees

1 30

2 50

3 28

4 38

5 40

6 50

7 46

8 20

9 22

10 40

T o t a l . . 3 6 4

A v e r a g e .

Animal 6. Anim al 10. Anima l 8. Animal 9.

Right lateral eye Right lateral eve Left lateral eye Left lateral eyegroup capped, group cappeo, group capped, group capped.

Deflection Defec tion Deflt 5onto left. to r ht.

degrees

Deflectionto right.

degrees

35

22

20

45

25

0

22

50

10

30

Deflectionto left. to right.

degrees degrees

25 9

36 .4 to r igh t . 25 .9 to r igh t .

Deflection Deflectionto left.

degrees

22

32

28

30

62

33

5

42

38

45

5 I 332

Deflt 5on Deflectionto r ht. to left.

degJ :s

32 .7 to l e f t .

degrees

20

0

40

30

30

20

10

20

0

2O

19 0

19 to lef t .

T A B L E I I .

Reactions to Balanced Illum inati on of A nima ls with Cutaneo us Photosensitive A reas

on One Side of Body Blackened. Measurements Recorded in Degrees of

Deflection fro m I niti al P ath o f Locomotion P erpen dicular to

Lin e Connecting Two Sources of Light.

Animal 21. Animal 22. Animal 23. Animal 24.

Cutaneous sensitive Cutaneous sensitive Cutaneous sensitive Cutaneous sensitiveareas on left side areas on left side areas on righ t side areas on righ t side

:No. of blackened, blackened, blackened, blackened.t r ia l

T o t a l . . .

A v e r a g e .

Deflection Deflectionto right, to left.

degrees degrees

1 12

2 26

3 12

4 13

5 30

6 28

7 36

8 50

9 48

10 31

286

28 .6 to l e f t .

Deflection Deflectionto right, to left.

degrees degrees

52

30

24

25

22

42

12

18

16

10

25 1

25.1 to lef t .

Deflection Deflectionto right, to eft.

degrees degrees

30

12

40

50

21

52 I

3o I22 '

28 t34 ~

i

31 9

31 .9 to r igh t .

Deflection Deflectio~to right, to left.

degrees degrees

30

20

56

24

34

60

20

20

16

24

30 4

30 .4 to r igh t .

44 2




BRADLEY M. PATTEN 443

TABLE I I I .

Summary of Measurements on Asymmetrically Blinded Animals under Balanced

Illumination.

Operation.

Deflections from init ialpat h of locomotion perpendicularto the line connecting two equally intense sources

of light at its m/d-point.

Individualaverages each ba~d on ten trials.- - ~ - - Average

Animals with right side Animals with left side deflectionless sensitive. ] less sensitive. [toward Jess

Deflections o right. Deflections to left. sensitive.] ] side.

One median eye capped.

Both lateral eye groups and median eye

on one side capped.

BoVh cutane ous sensit ive areas a nd

both lateral eyes blackened and

median eye on one side capped.

One lateral eye group capped.

Cutaneo us sensitive areas on one side

blackened.

Both lateral eye groups and both

median eyes capped and cutaneous

sensitive areas of one side blackened.

One median eye and one lateral eye on

same side capped.

One median eye and the cutaneous sen-

sitive areas on the same side black-

ened.

One lateral eye and the cutaneous sen-

sitive areas on the sam e side black-

ened.

degrees

15.6

17.9

27.1

28.5

29.0

36.0

37 .6

36.9

43 .9 ¸

All photorece ptors on one side black- Circus

ened. move-

ments.




444 PHOT OR]~ ACTI ONS Ol WI-IIP-TAIL SCOR PION S

The measurements g iven in Tables I to I I I a re g raphical ly summar-

ized in Fig. 3. The circles represe nt the ob serva t ion circle of theappara tus , and the groups of ar rows the d irec t ion of the l igh ts . The

ini t ial posi t ion of the animal is indicated by the out l ine in the center

of the circle, and the average path of an animal , based on ten t r ials ,

by the radial arrows. On the same figure the average pa th of t ravel

fol lowed by norm al animals , under the same ex perimen tal condit ions,

is indicated by shading. The arrows showing deflect ions to the right

and to the left indicate the courses of animals with the blackening

carried out on their r ight and on their left s ides respect ively.

In every one of the ten combinat ions of el iminat ions in which the

photorecep t ive mechanism was l ef t funct ional ly asymmet r ica l , the

deflect ion appeaxs toward the s ide ma de less sensi t ive.

Reactions to Balanced Opposed Illum inatio n o f An ima ls Subjected to

Symmetrical Interference with the Receptive Mechanism.

As cont ro l s to the exper iments in which the recep t ive mechanism

was rendered funct ional ly asymmet r ica l , measurements were made

covering the react ions to balanced i l luminat ion of animals which had

been subjecte d to bi lateral ly symm etrical el iminat ions of their l ight-

sensi t ive organs.

The measurements are summarized in Table IV and represen ted

graphical ly in Fig. 4. The man ner of repre sentat ion is the same as

that in Fig. 3, the shaded area represent ing the react ion range of nor-

mal animals , and th e radial a rrows the average paths of the experi-men tal animals . In none of the cases do the react ions of animals with

the photosens i t ive mechanism lef t funct ional ly symmet r ica l vary

appre ciably from the react ions of norm al animals . This series of

measurem ents s t ands in s t r ik ing co nt ras t to tha t o f Fig . 3 wi th which

i t should be compared.

Reactions to Lateral and to Anterior Illumination of Animals Subjected

to Symmetrica l Interference with the Photoreceptive Mechanism.

While symm etrical ly bl inded animals showed l i tt le or no variat io n

from the normal when subjected to balanced i l luminat ion, under lateral

or anterior i l luminat ion their at tainment of orientat ion was retarded.




o I, .¢ 0

I

I

.,.a

o .~

e ~ , a ~

4. a

g~

" ~

. ~

0 0

• ~.~

0 0~

"~

o ~ o

• ~ . ,q

. . 4 . a

V

~ o ~° -~ °~.~

~ . o .




BRADLEY M. PATTEN 44 5

T h i s d i f f er e n c e i n r e s p o n s e i n t h e t w o c a s e s i s d u e t o t h e d i f f e re n c e i n

t h e w a y t h e a n i m a l s w e r e b r o u g h t i n t o t h e f ie l d o f l i g h t. W h e n s u b -j e c t e d t o b a l a n c e d i l l u m i n a t i o n , t h e i r i n i t i a l d i r e c t i o n o f l o c o m o t i o n

w a s " i n o r i e n t a t i o n " a n d i t w a s o n ly n e c e s s a r y t o m a i n t a i n i t . T h e

s y m m e t r i c a l l y r e d u c e d p h o t o s e n s i t iv e m e c h a n i s m d i d t h is n e a r l y a s

e f f e c t i v el y a s t h e n o r m a l . U n d e r l a t e r a l o r a n t e r i o r i l l u m i n a t i o n t h e

TABLE IV.

Reactions to Balanced Illumination of Anim als Previously Subjected to Symmetrical

Interference with Photoreceptive Mechanism.

Operation.

Both median e y e s

capped.

Both lateral e y e s

capped.

Cutaneous sensitive

areas on both sidesblackened.

Both median and both

lateral eyes capped.

Both lateral eyes

capped and cutane-

ous sensitive areas

on both sides black-

ened.

Deflection rom nitialpath of locomotion perpendicular to line connectingtwo equally intense sources of lightat its mid-point.

Individual verages based on ten trials. Average path

of all animalsAnimal 1. An im al. Animal. Animal. tested.

degrees

0.3 to fight.

2.3 to left.

0.2 to left.

4.2 to fight.

2.1 to fight.

degrees

0.8 to left.

2.9 to left.

3.9 to fight.

4.7 to left.

4.7 to fight.

degrees

0.1 to left.

3.5 to right.

4.3 to fight.

3.7 to right.

4.9 to right.

degrees

0.3 to right.

1.6 to right.

0.6 to fight.

0.2 to right.

3.0 to left.

degrees

0.1 to left.

0.03 to left.

2.1 to right

0.9 to right

2.2 to right

a n i m a l m u s t change its direction of locomotion to come into orientation,

a n d t h i s w a s a c c o m p l i s h e d l e ss r a p i d l y in a n i m a l s w i t h r e d u c e d p h o t o -

s e n s i t i v e a r e a s t h a n i n n o r m a l i n d i v i d u a l s . D o u b t l e s s i f t h e fi n a l

o r i e n t a t i o n w er e m e a s u r e d , i t w o u l d v a r y b u t l i tt l e f r o m t h a t o f

n o r m a l a n i m a l s . S i n c e, h o w e v e r , t h e r e a c t i o n s a r e m e a s u r e d b y

p o i n t o f e m e r g e n c e f r o m a s t a n d a r d c i rc l e, e v e n s l i g h t v a r i a t i o n s i n t h e

r a t e o f c o m i n g in t o o r i e n t a t i o n b e c a m e a p p a r e n t , b e c a u s e t h e m e t h o d




446 P t t O T O I ~ E A C T I O N S O F WHIP-TAIL S C O R P I O N S

was based on the degree of orientation attained while the animal was

traveling over a standard distance, thus taking into account the timefactor.

I I

a. b , C,

d . e .

FIG. 4. Graphical summary of reactions to balanced illumination in animals

which had been subjected to symmetrical interference with their photoreceptive

mechanism. The circle represents the observation circle of the apparatus; the

groups of arrows, the direction of the light beams; the silhouette of the scorpion,

the animal 's position when subjected to bilateral illumination; the shaded seg-

ment, the average path of normal animals; the curved radial arrows, the average

paths of experimental animals (.based on ten trials), a. Animals with both median

eyes capped, b. Both lateral eye groups capped, c. Cutaneous sensitive areas

on both sides blackened, d. Both lateral and both median eyes capped, e.

Both lateral eyes and the cutaneous sensitive areas on both sides blackened.

The reaction measureme nts made on symmet rically blinded ani-

mals subjected to lateral illumination are collected in Table V and in

Fig. 5. The solid arrows represent the average path followed by the

partially blinded animals, the dotted arrows the average reaction of

normal animals under the same conditions of illumination.




BRADLEY M. P A T T E N 447

T A B L E V .

Reactions to Lateral Illumination of Animals Previously Subjected to SymmetricalInterferen ce with Photoreceptive Mec han ism.

Oper a t ion .

Bo th m ed ian ey es cap p ed .

Bo th la te ra l ey es cap ped .

Cutaneous sensit ive areas of both s ides

blackened.

Bo th med ian an d b o th la te ra l ey escapped.

Def lec t ion f r om in i t i a l pa th o f locom ot ion a t r igh tang le s ac r oss the b eam of l igh t .

Anim a l I . An im a l 2 .

d~re~ degre~

61.3 61.9_ _ ] _ _

4 3 .5 5 0 .5

60.1 48.1

Bo th la te ra l ey es cap p ed an d cu tan eo u s

sensit ive areas of both s ides b lackened.

All photoreceptors b lackened.

I nd iv idua l ave r ages ba s ed on t en t r i a l s. Ave r age o2

all animal.,tested.

5 2 .5 4 1 .3

4 2 .6 3 0 .4

+ 8 . 8 * 6 . 3

Anim a l 3 . Anim a l 4 .

degrees degrees

58.3 55.2

6 0 .3 6 7 .4

3 8 .9 4 5 .1

3 9 .5 4 4 .2

4 4 .6 2 3 .8

4 . 6 2 . 0I

degrees

39.2

5 5 .4

48.1

4 4 .4

3 5 .4

1 .0

T h e p l u s s i g n i n d i c a t e s t h a t t h i s d e f l e c t i o n w a s toward t h e l i g h t. A l l o t h e r d e -

f l e c t i o n s i n t h e t a b l e a r e a w a y f r o m t h e l i g h t , o r n e g a t i v e .

T A B L E V I .

Reactions to Anterior Il lumination of Animals Previously Subjected to Symmetrical

Interference with Photoreceptive Mechanism.

Oper a t ion .

Both median eyes capped.

Both la tera l eyes capped.

Zutaneous sensit ive areas of both s ides

blackened.

Bo th la te ra l an d b o th med ian ey es

capped.

Both la tera l eyes capped and cut aneous

sensit ive areas on both s ides b lack-

ened.

Def lec tion f r om in i t i a l pa th o f locom ot ion d i r ec t lytowar d s our ce o f l igh t .

I nd iv idua l ave r ages ba s ed on t en t r i a l s. Ave r age o f

all animals

Anima l 1. Anima l 2. tes ted.

degrees

117.3

124.9

Anim a l 3 .

de~ees d~rees

123.5 136.6

128.8 127.8

Anim a l 4 .

d~re~

132.6

140.9

120.2 121.0 101.2 100.4

118.3 116.0 108,3 115.8I

8 8 .8 9 8 .4 1 0 1 .09 1 . 3

degrees

127.5

130.6

1 1 0 . 7

114.6

9 4 .9




448 P H O T O R E A C T I O N S O F Wi-IIP-TAIL SC OR PI ON S

T a b l e V I a n d F i g. 6 sh o w t h e re a c t i o n s o f s y m m e t r i c a l l y b l i n d e d

a n i m a l s t o a n t e r i o r i l l u m i n at i o n . T h e e x p e r i m e n t a l c o n d i t io n s u n d e rw h i c h t h e s e m e a s u r e m e n t s w e r e m a d e a r e e s s e n t i a l l y s i m i l a r t o t h o s e

I I

1

a , b . C .

d. e. f.

FIG. 5. R eactions to lateral illumination in animals which had been subjected

to symm etrical interference with their photo receptive mechanism. The circle

represents the observation circle of the app aratus; the group of arrows, the direc-

tion of the light beam ; the silhouette of the scorpion, th e anim al's position when

subjected to lateral illumination; the do tted arrow, the average reaction of nor-

mal animals; the solid arrow, the average reaction of the experimental animals.

a. Animals with both m edian eyes capped, b. Ani mals w ith both lateral eye

groups capped, c. Cutaneous sensitive areas on both sides blackened, d.

Both m edian and both lateral eyes capped, e. Both cutaneous sensitive areas

and bo th lateral eyes blackened, f . All photoreceptors blackened.

s e t u p w h e n l a t e r a l i l l u m i n a t i o n w a s u s e d . T h e d i f f er e n c e l ie s o n l y

i n t h e g r e a t e r d e f le c t io n a n a n i m a l m u s t m a k e t o c o m e i n t o o r i e n t a -

t i o n w h e n s u b j e c t e d t o a n t e r i o r i l lu m i n a t i o n . A c o m p a r i s o n o f F i g s .




449

e°

5 a n d 6 s h o w s t h a t t h e r e a 6 t i o n s u n d e r l a t e r a l a n d u n d e r a n t e r i o r

i l l u m i n a t i o n a r e q u a l i t a t i v e l y t h e s a m e .Q u a n t i t a t i v e c o m p a r i s o n b a s e d o n t h e p e r c e n t a g e r e d u c t i o n o f

t h e n o r m a l r e a c t i o n i n e a c h c a s e s h o w s a c o r r e s p o n d e n c e w h i c h i s

L ight !2 0 C ~ o

i

b.C.

d.

BRADLEY M. PATTEN

Fro. 6. Reactions to an terior illumination in animals which had been subjected

to symm etrical interference with their photoreceptive mechanism. The circlerepresents the observation circle of the ap paratu s; the group of arrows, the direc-

tion of the light beam ; the silhouette of the scorpion, the an imal's position when

subjected to anterior illumination; the dotted arrow, the average reaction of nor-

mal animals; the solid arrow, the average reaction of the experimental animals.

a. Animals with both median eyes capped, b. Animals with both lateral eyes

capped, c. Cutaneous sensitive areas on both sides blackened, d. Both median

and both lateral eyes capped, e. Bo th cutaneous sensitive areas and b oth lateral

eyes blackened.

w i t h i n t h e l i m i t s o f e x p e r i m e n t a l e r r o r , w h e n t h e d i f f e r e n c e s i n e f fe c -

t i v e i l l u m i n a t i o n d u e t o t h e a n a t o m i c a l p o s i t i o n o f t h e r e c e p t o r s i s

t a k e n i n t o c o n s i d e r a t i o n ( s ee b e l o w ) .




450 PHOTO REACTI ONS OF V~=~_IP-TAIL SCORPI ONS

DISCUSSION.

Relative Effectiveness of Photoreceptors.

The relative effectiveness of the lateral eye groups, the median

eyes, and the cutaneous photosensitive areas should be indicated by

the changes from the normal reactions produced by their elimination.

Table VII is a summary of the data secured by unilateral and bilat-

eral elimination of each of the photoreceptors. The change from the

normal reaction is given (1) in degrees of deflection; (2) in per cent

TABLE VII ,

Summary of Effects of Eliminating Different Members of Photoreceptive Mechanism.

Organeliminated.

One median

eye.

3ne lateral

eye.

Dne cutane-

ous sensi-

t ive area.

Unbalance as

measured underbilateral illu-

mination.

degrees

15 .6

28 .5

29 .0

~-~ .

>.o=~

1 .0

1 .8

1 .9

Pair of organseliminated.

Both median

eyes.

Bo th la te ra l

eyes.

Bo th cu tane-

ous sensi-

t ive areas.

Reduction from normalreaction as measured un-der l ateral illumination.

~ ~g~ .-~

6 .6 10

10 .4 15 .9

17 .7 26 .8

1 .0

1 . 6

2 . 6

Reduction from normalreaction as measured un-der anterior llumination.

~.~ ~ ~.o

12 .9 9 .2

9 . 8 7 . 0

297 ] 212

1. 0

0 . 8

2 . 3

of the normal reaction; and (3) in relative values calculated by taking

the change produced by elimination of the median eyes as unity.

There are certain apparent inconsistencies in the data of Table VI I

that require consideration before we attempt to draw any conclusions

as to the relative effectiveness of the photoreceptors.

There is good agreement between the reductions in normal reaction

produced by the elimination of the median eyes under lateral and

under anterior illumination, the value of the reduction from normal

being 10 per cent under lateral illumination and 9.2 per cent under




BRADLEY M. PATTEN" 451

anter ior il luminat ion. The changes f rom the no rmal reac t ion in-

duced by el iminat ion of the lateral eyes, however, do not show thesame consistency, the values being 15.9 per cen t reduct ion of the nor-

mal react ion un der lateral i l luminat ion, and 7 per cent reduct ion

und er anterior i l luminat ion. This discrepancy is, I bel ieve, at t ribu t-

able to the anatom ical locat ion of the lateral eyes. The ir posi t ion at

the sides of the cephalothorax, surrou nded b y heav ily pigm ented

chit in, is such that a very small proport ion of the l ight in the field

wo uld be effective on th e retinula~ of the lateral ey es w hen t he a.n]mal

is direct ly facing the l ight . Th e lateral eyes would, therefore, be op-

erat ing below their capaci ty durin g a considerable par t of the deflec-

t ion made by animals headed into the light. On the other hand, th ey

would be opera t ing a t maxim um eff ic iency dur ing the g rea te r par t of

the deflect ion ma de by animals subjected to lateral i l luminat ion.The median eyes are so placed that they receive approximately the

same am ou nt of effect ive i l luminat ion wheth er the animal is sub-

jected to anterior or to lateral i l luminat ion. Th e condit ions of shad-

ing, involved in the ini t ial posi t ions of the animal account , therefore,

for the discrepancy in the two sets of react ion meas urem ents mad e on

animals with their lateral eyes covered. The sam e considerat ions

would indica te tha t measuremen ts under l a te ra l i l lumina t ion express

more correct ly than experiments under anterior i l luminat ion the rela-

t ive effect iveness of the p hotoreceptors.

Another apparent incons is tency in the da ta of Table VII i s revea led

by adding the reduct ions in deflection prod uced by the separate el imi-

na t ion of each receptor . Taking as a basi s the measurements made

under lateral i l luminat ion, the reduct ions in deflect ion caused by the

separate el iminat ion of the three photoreceptors total to a value ap-

proximate ly only one-ha l f the normal reac t ion; ye t when the three

receptors are simultaneou sly el iminated the animals are pract ical ly

insensi t ive to l ight (Table V and Fig. 5). It is possible to at t ribu te

these condi t ion s to a compensa tory increase in ac t ivi ty on the par t

of the unblacken ed receptors. While this ma y be in par t responsible,

I bel ieve the greater part , a t least , of the discrepancy can be other-

wise explained. In each of the series of meas urem ents in which some

part of the photorecept ive mechanism is prevented f rom func t ioning,

the reduct ion in deflect ion is measured at what mig ht be cal led the




45 2 PIIOTO I~EACT IONS OF VCI-IIP-TAIL SC OR PI ON S

uppe r end of the deflection range. I t has been shown (1) tha t the

increase in i l luminat ion necessary to produce an ini t ial deflect ion ofdefini te va lue is less than the increase in i l luminat ion nece ssary

to prod uce an increase in deflect ion of l ike value. Th e da ta col-

l ec ted were no t suffi c ien t ly ex tens ive to jus t i fy the s ta tem ent

tha t the increases in def lec t ion fo l lowed mathem at ica l ly th e Weber-

Fechner l aw, bu t the curve of increase in def lec t ion wi th in -

creasing lateral i l luminat ion is certainly of tha t general type. Ap-

pl ied to the da ta under c onsiderat ion, this means th at the fi rs t 10 ° of

deflect ion are more readi ly induced than the deflect ion from 10 ° to 20 °

and so on. A re duct ion in deflect ion to 50 ° from a normal of 60°,

fol lowing interference with receptors , does not indicate therefore that

the recep t ive mechanism has been reduced by one-s lx th in ef f i c iency .

On the cont rary , i t would requi re a reduct ion of cons iderab ly morethan one-sixth in photorecept ive effect iveness to reduce by one-sixth

the normal react ion.

While i t is not possible, in the l ight of the above considerat ions, to

compute the effect iveness of the different receptors on the basis of

the percen tage reduct ion of normal react ions produc ed by thei r el imi -

nat ion, their relat ive effect iveness ma y, nevertheless , be deduc ed from

the avai lable data. All the induced reduct ions in react ion, because

of the method of measurement employed , fa l l in the same par t o f the

deflect ion range. Th ey can, therefore, just i f iably be com pared with

each o ther . This compar i son has been worked ou t in Table VII b y

tak ing the ef fec t o f the e l iminat ion of the median eyes as un i ty and

compar ing wi th i t the ef fec t p roduced by e l iminat ion of the o ther

recep tors . By averag ing ~ the values thus o b ta ined und er the th ree

different condit ions of i l luminat ion used, we can approximate the rela-

t ive ef fec tiveness of the photorecep tors as median eyes : l a tera l e yes :

cutaneous areas :: 1: 1.6: 2.2.

3 In computing the averages the responses to anterior illumination made b yanimals with their lateral eyes capped were not given equal weight with thosemade under lateral illumination. The reasons for regarding the experiments un-der anterior illumination as les s accurate as far as indicating the effectiveness ofthe lateral eyes is concerned, are g iven in the text.




BRADLEY ~. PATTEN 453

Effect on Orientation Produced by Symmetrical and by Asymmetrical

Interference with the Photoreceptive Mechanism.

Smal l changes in the tonus of the musc les of locomot ion a re f re -

que nt ly di f f icul t to de tec t and a lways di f ficult to handle q uant i ta t iv e ly

in an animal which i s not moving. An animal ' s locomot ion, however ,

i s a d i rec t r esul tan t of muscula r ac t iv i t ies and any di f fe rence in the

tonus or in the vigor of cont rac t ion of the musc les on opposi te s ides

of the bo dy i s a t once evidenced by a def lec tion in the p a th of advance .

Smal l d i f fe rences in c ont rac t ion a re sum mate d in con t inued locomo-

t ion. The mea surem ent of def lec t ions in the pa th of t r ave l is , the re -

fore , a convenient and accura te method of dea l ing quant i ta t ive ly

wi th the ac t iv i ties of locomotor musc les .

Unbalanced muscula r r eac t ions as indica ted by a curved pa th oflocomot ion have been observed to fol low uni la te ra l b l inding in both

posi t ive ly and nega t ive ly photot ropic animals. The ear lie r observa-

t ions were qua l i ta t ive only , more recent ly the reac t ions have been

qua nt i ta t ive ly handled. In a ll the cases the evidence i s in accord

wi th Loeb ' s musc le tens ion theo ry of or ienta t ion, pos i t ive ly photo-

t ropic forms moving in curves wi th the i r unin jured s ide inward, and

nega t ive forms in curves wi th the i r b lackened s ide inward (4) .

The reac t ion measurements made in te rms of angula r def lec t ion on

part ial ly blinded whip-tai l scorpions fal l entirely in l ine with observa-

t ions on other animals. Bu t because the scorpion has three pa i r s of

photoreceptors , each of which can be e l imina ted separa te ly , th e se ries

of meas urem ents which can be ma de on i t i s pecul ia r ly extens ive and

interest ing. I t is possible to el iminate on one side of the bo dy th e

median eye , the la te ra l eye , or the cutaneous sens i t ive a reas ; or any

two receptors ; or a l l three receptors . By m aking e l imina t ions on both

sides of the body, the ser ies of cases may be st i l l fur ther extended.

In these exper iments measurements were made , under bi la te ra l ly

ba lanced i l lumina tion, o n animals in ten di f fe rent condi t ions of asym -

metry . The resul t s a re col lec ted in Table I I I . The graphica l sum-

m ary (F ig . 3) shows dear ly the uner r ing consis tency wi th which a l l

the anim als were def lected tow ard their less sensit ive side. All the

deflections are to be regard ed as havin g the sa me signif icance as cir -

cus mov ements . In mo st of the deflec tions the radius of the curved




45 4 P H O T O P , , E A C T I O I ~' S O 1 W H I P - T A I L S C O R P I O N S

path fol lowed by the an imals is greater than the radius of the observa-

t ion c irc le of the appara tus . Whe n the induced asymm et ry is ex-treme, typical circus mo vem ents of small radius resul t . The poin t of

emergence of the t rai ls of larger radius on the s tandard observat ion

circle, gives an index of the curvature of the arc of locomotion in

quant i t a t ive t erms which are comparab le wi th the o ther react ion meas-

urements . The cons tan t curv ing of the pat h of locomot ion in an i-

mals which are asymmet r ica l ly sens i t ive s tands in sharp cont ras t to

the locomotion of norm al animals under bi lateral ly uneq ual i l lumina-

t ion. In the lat ter case the pat h of locomotion is s t raight onc e the

direct ion of crawling becomes such that the inequal i ty in i l luminat ion

in the field is equal ized in i ts effect iveness on the photosensi t ive areas

of the animal by greater exposure of the sensi t ive areas on the s ide of

less intense i l luminat ion, and lesser exposure of the sensi t ive areas onthe s ide of more intense i lluminat ion (5). Asy mme trical ly sensi t ive

animals under ve rt ical i l lumin at ion cont inue in a curving pa th

of locomotion becau se i t is impossible through changes in axial posi-

t ion to equal ize bi lateral ly the effect ive i l luminat ion. Un der eq ual

and op posed horizontal i l luminat ion s l ight bi lateral inequal i t ies in

selasi t iveness may be compensated for by the assumption of an axial

posi t ion incl ined towa rd the less intense l ight . Wh en the asy mm etr y

of sensi t iveness is mad e extre me the effect ive i l luminat ion ca nnot thus

be brought in to b i l a tera l equ i l ib r ium and the curved path of locomo-

t ion is cont inued.

A feature deserv ing fur ther comment i s the way in which the am-

pli tude of the deflect ions increases as the degree of asym me try in

sensi t iveness is increased. The cumula t ive effect prod uced b y black-

ening more than one receptor on the same side of the head is obvious

from the figures . Less appa rent bu t equal ly s ignificant is the fact

that the unbalance in react ion is g reater when a l l the recep tors except

a given one are el iminated, than when the sam e receptor is the only

one covered. Fo r example, the deflect ion induced when the media n

eye on one s ide is capped averages 15.6°; when both lateral eyes, the

cutane ous sensi t ive areas on bot h s ides, and the media n ey e on one

side are blacken ed (leaving funct ional on ly one med ian eye), the de-

flect ion averages 27.1 ° (see Table III) . The u nbala nced f actor in each

experiment is a median eye, but when the median eye alone is el im-




BRADLEY M. PATTEN 455

ina ted the ba lance of the recept ive mechanism as a whole i s less d is -

turbed than when the median eye on one s ide i s the only func t iona lreceptor .

I t i s not per t inent here to ente r in to a de ta i led compar ison of these

resul ts on the scorpion wi th the exper im ents of Gar rey (6) on the

posi t ive ly photot ropic robber f ly , but the comple te agreement of the

two se r ies of observa t ions mad e by di f fe rent methods , on anim als

having opposi te s igns of photot ropism, i s too s t r ik ing to pass wi th out

c omme nt .

Fur ther evidence tha t ba lanced reac t ions depend on the func t iona l

sym me t r y o f t he r e c ep t i ve me c ha n i sm i s f u r n ishe d by t he me a sur e -

me n t s ma de on a n ima l s i n w h ic h t he pho to r e c e p to r s ha d be e n sym-

metr ica l ly in te r fe red wi th . As in the case of asym metr ica l ly sens it ive

scorpions, th e sym metr ica l ly bl inded animals were broug ht in to th ef ield of equal opposed l ights " i n or i e n t a t i on" (i.e., with the i r p lane of

sym me try perpendicula r to the l ine connec t ing the sources of light ) .

No ma t te r w hat e l imina t ions were made , so long as the photorecept ive

mechanism was le f t in a func t iona l ly symmetr ica l condi t ion i t suf -

f iced to m ainta in 4 a ba lanced response which was accura te wi thin the

l imi ts of var iabi l ity exhibi ted by norm al animals under the same con-

dit ions of i l lumination (Table IV and Fig. 4) .

Observa t ions a l ready publ i shed by many di f fe rent inves t iga tor s

have covered near ly every phase of the cor re la t ion exis t ing be tw een

bi la te ra l ly ba lanced exc i ta t ion of photoreceptors and ba lanced loco-

mo tor responses. A co nstant ly increas ing accumula t ion of exper i-

men ta l evidence indica tes tha t th e a t ta ining a nd m ainta ining of or i-

enta t ion to l ight depends , as pos tula ted in Loeb ' s musc le tens ion

theory, on the t r ansmiss ion to the musc les of locomot ion of impulses

which a re propor t iona l b i la te ra l ly to the exc i ta t ion of symmetr ica l ly

loca ted photoreceptors .

The resul t s of the exper iments descr ibed above indica te tha t the

musc le tens ion theory appl ies to the complex recept ive mechanism of

4 It has already been pointed out t hat when brought into the field of light outof orientation (as in the experiments under anterior and lateral illumination)symmetrically blinded anim als exhibited a retardation in their rate of comingto a new direction of orientation.




BRADLEY M. PATTEN" 45 7

The react ions of an imals thus par t i a l ly b l inded were measured in

terms of angular deflect ion from an ini t ial path of locomotion. Mea s-urements o b ta ined under an ter io r , l a tera l, and b i l a tera l ly balanced

i l luminat ion were compared wi th measureme nts made on normal an i -

mals unde r the same condit ions of i l luminat ion. Th e change from the

normal react ion induced by cover ing a photorecep tor was t aken as an

index of the effect iveness of the receptor prevented from funct ioning.

By compar ing the values o f the changes f rom normal react ions pro-

duce d by the el iminat ion of the several receptors , their relat ive effec-

t iveness i s approxim ated as m edian eyes : l a tera l eyes : cu taneous

sensi t ive areas : : 1 : 1.6 : 2.2 .

All an imals in which the recep t ive mechanism was rendered func-

t ional ly asym met r ica l exh ib i ted , when sub jected to b i l a tera l ly bal -

anced i l luminat ion, deflect ions toward the s ide which had been madeless sensi t ive. In a series of mea surem ents mad e on animals in ten

d i f feren t condi tions of asy mm et ry the ampl i tudes of the def lec t ions

were propor t ional to the degree of unbalance which had been produced

in the photosens i t ive mechanism.

Animals in which the recep t ive mechanism w as reduced bu t l ef t in a

symmet r ica l condi t ion main ta ined an undis tu rbed balance of reac-

t ion when sub jected to equal , opposed light s . Under l a tera l o r an-

terior i l luminat ion the rate of at taining a new direct ion of orientat ion

was reduced in p ropor t ion to the ex ten t o f the in ter ference wi th the

recep t ive mechanism.

The react ions of symmet r ica l ly and asymmet r ica l ly b l inded scor-

p ions ind icate tha t o r ien ta t ion i s a t t a ined and main ta ined by a t rans -

mission of impulses to th e muscles of locomotion which is proport io nal

b i l a tera l ly to the exci ta t ion of the symmet r ica l ly located photo-

receptors .

In their effect on orientat ion the three pairs of receptors are com-

pletely coordinated. Orienta t ion depen ds upon bringing the exci ta-

t ion of the recept ive mechanism as a whole into bi lateral equi l ibrium.

BIBLIOGRAPHY.

1. Patten, B. M., J. Exp. Zool., 1917, xxili, 251.2. BSrner, C., Zoologica, 1904, xvii, No. 42, 1-174 .3. Patten, B. M., Science, 1915, xli, 141.




458 PHOTO!~ACTI01WS OF V~I-IIP-TAIL SCORPIONS

4. Loeb, J., Forced movements, tropisms, and animal conduct, Philadelphia and

London, 1918.

5. Patten, B. M., J. Exp. Zool., 1914, xvii, 213.

6. Garrey, W. E., Proc. Nat. Acad. Sc., 1917, iii, 602; J. Gen. Physiol., 1918-19,

i, i01.


PHOTOREACTIONS OF PARTIALLY BLINDED WHIP-TAIL

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