DescriptionPSM V84 D531 Facts and factors of development fig3-5.jpg
Fig. 3. Entire spermatozoon of the annelid nereis, showing perforatorium (P); head (H); middle piece (M), and tail (T). (From F. R. Lillie)
Figs. 4-5. Two stages in the entrance of the spermatozoon into the egg of nereis. Some of the protoplasm of the egg has gathered at the point of entrance to form the entrance cone (EX) which, together with the sperm head, moves into the interior of the egg in the later stages. The black spheres represent yolk. (From F. R. Lillie)
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