368 IvTaoliide Yatsn. 



zoon (PI. II, Fig. 10) the head is composed of two parts; a fine 

 anterior pi-ocess and a posterior broader part. The middle-piece is 

 much more vesicular than that of the full grown ones. In still 

 younger ones (PI. II, Figs. 17 and 18) the head is almost spherical 

 and is prolonged anteriorly into a short process. The centriole is 

 present at the posterior end of the protoplasmic covering. After pierc- 

 ing through the egg-membrane the spermatozoon bores into the egg, 

 where a little depression is seen. Then the head shoots into the 

 ooplasm with a whip-like movement of the tail'" and the latter is 

 quickly drawn in.^"* In many cases the spermatozoon rotates nearly 

 180°. Very little locomotion takes place within the egg, judging 

 from the fact that all the stages of the formation of the sperm- 

 nucleus,^"^ and of the sperm-asters are found near the periphery of 

 the egg. 



"One may observe a sawing movement of the head, as it gradually pushes 

 in before its final shooting-in. After piercing through the egg membrane, quite 

 often the spermatozoa are found again boring into the membrane from inside 

 instead of into the egg. It sliould also be noted that spermatozoa are sometimes 

 found boring into the fertilized eggs or even the blastomeres of the two-cell 

 stage. This clearly shows that the spermatozoon has no power of distinguish- 

 ing the non-fertilized from the fertilized eggs, and that the attraction of the 

 spermatozoon to the egg, at least in the vicinity of the egg, is not due to 

 chemotaxis. 



"In sections the tail is seen in the egg as described by Kostanecki '02, p. 

 273). One notices that it has shortened a great deal. Whether a part of the 

 tail is lost at the entrance or is dissolved in the egg, or whether it contracts I 

 have not been able to determine. But it is noteworthy that it increases in its 

 staining capacity after entering the egg (Kostanecki and Wlerzejski, '90, p. 

 336). The tail is sometimes straight (PI. II, Fig. 27), sometimes it bends on 

 itself (PI. II, Fig. 2G). From this and the fact that in some molluscau eggs the 

 spermatzoon is found coiled up, it may be inferred that the sperm may move 

 in the egg. In fact, by careful watching of the egg of Ccrehratulus, it may be 

 observed by the disturbance of the yolk granules that the spermatozoon wriggles 

 for a little while before it becomes quiescent. 



"The sperm head shortens after its entrance into the egg (PI. II, Fig 24). 

 A construction appears between the head proper and anterior process (PI. II, 

 Fig. 25). Then the chromatin seems to be drawn into the head proper from 

 the anterior process, which gradually loses its staining cai)acity. The head 

 proper becomes more and more spherical as the anterior process becomes 

 thinner (PI. II, Figs. 20-28). Finally the latter disappears (PI. II, Fig. 29>. 

 It may be i)ointed out that in the egg the sperm-head repeats in reversed order 

 what it did during the later stages of its growth. The curved slender head. 



