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Microtome for cutting ultrathin tissue sections

Panulirus interruptus, the California spiny lobster

Stomatogastric ganglion

Synaptic contacts within a small region of nervous tissue

Shape of one nerve cell

(in lobster stomatogastric ganglion)

Reconstructing cell shape from sections

Drosophila melanogaster, the laboratory fruit fly

Head

Thorax

Abdomen

the cardia in the fly digestive tract

Elaboration of cardia structure, along the main line of fly evolution

in cross section of fly nerve cord“Giant” nerve fibers ( * )

Giant fibers conduct signals from antennae to flight muscles.

Drosophila melanogaster

Muscina pascuorum

Minettia magna

Fly species differ in their distributions of nerve-fiber diameter.

Tipulidae, Tipula bicornis Forbes Lauxaniidae, Minettia magna (Coquillett)

Tabanidae, Tabanus calens Linnaeus Syrphidae, Helophilus fasciatus Walker

Bombyliidae, Sparnopolius sp. Bombyliidae, Poecilanthrax sp.

How can evolution adjust the properties of individual nerve cells?

Charles Darwin Letter to T.H. Huxley 1859

One point which has greatly troubled me; . . . what the devil determines each particular variation? What makes a tuft of feathers come on a cocks head, or moss on a moss rose?