div class=trans-pagebuttonPage 1button div class=trans-image amp-img class=trans-thumb alt=Page 1: X and Y Spermatozoa src=https:reader036fdocumentsinreader036viewer2022081201575068161a28ab0f07ae8994html5thumbnails1jpg width=142 height=106 layout=responsive amp-img divp© 1960 Nature Publishing Grouppdivdiv class=trans-pagebuttonPage 2button div class=trans-image amp-img class=trans-thumb alt=Page 2: X and Y Spermatozoa src=https:reader036fdocumentsinreader036viewer2022081201575068161a28ab0f07ae8994html5thumbnails2jpg width=142 height=106 layout=responsive amp-img divp© 1960 Nature Publishing Grouppdiv