280 DR. J. B. GATENBY ON THE GERM-CELLS AND 



cleavage-stages I have come to the conclusion that the sperm-carrying cell 

 either wanders away after the spermatozoon has passed out of its cytoplasm, 

 or in some way effaces itself by degenerating or shrinking in size. I found 

 only one case suggesting that the sperm-carrying cell subsequently degene- 

 rates : in PI. 21. fig. 18, the cell at SCO is obviously unhealthy. At present 

 I am led to consider that the sperm-carrying cell subsequently wanders away 

 through the mesoglea. 



22. Behaviour of Sperm and Sperm-bearing Cell explicable as a 

 Chemotactic Phenomenon. 



In text-fig. 4 is drawn diagrammatically a part of an oocyte and the neigh- 

 bouring row of collar-cells. Twenty-five oocytes were examined at the stage 

 of fertilization drawn in text-fig. 3, and the position of the sperm was 

 indicated in the diagram in fig. 4 by a black dot. This diagram, therefore, 

 gives a graphic representation of the fact that the swimming spermatozoon 

 is definitely attracted in some way towards the egg. If this were not so, one 

 would not find the sperm almost invariably entering cells neighbouring the 

 egg. I have not found sperms in collar-cells further away from the egg 

 than those drawn on the extreme left and right in fig. 4. 



Chemotaxis as an explanation of the attraction of any sperm by any egg 

 has been abandoned to a great extent by zoologists, but surely here is a 

 definite case of attraction between egg and sperm ? The egg of the sponge 

 seems able to give forth some substance which causes the sperm to swim to 

 that region of the gastral epithelial carpet which just overlies an oocyte. I 

 cannot think of any other explanation which accounts for text-fig. 4 so 

 satisfactorily. 



23. The Entry of the Spermatozoon into the Egg and the Effect on 



both. Gametes. 



The sperm is drawn into the unmatured oocyte probably by synchronous 

 flowing movements of the protoplasm of both sperm-carrying cell and the 

 oocyte. That the sperm itself has no immediate part in the process seems 

 indicated by the fact that it is able to pass into the egg with its nucleus 

 forwards or its middle-piece forwards (PL 20. fig. 11) or sideways. There 

 is undoubtedly a complete protoplasmic continuity established between the 

 cytoplasm of the carrier-cell and that of the oocyte ; here the vitelline 

 membrane of the egg is interrupted as shown in PL 20. figs. 12 and 14. 



When the sperm has passed into the egg, the first change noticed in it is 

 the breaking-down of the sperm-cell wall (PL 20. fig. 16). The acrosome 

 (AC) becomes faint, and is just disappearing in the last figure. The sperm 

 cytoplasm becomes furred at its edges where it touches the egg-cytoplasm ; 

 soon a flowing movement, apparently initiated by the entiy of the sperm, 

 tends to disturb the arrangement of mitochondria, which partly pass to that 

 hemisphere of the oocyte at which the sperm entered (PL 20. figs. 10, 12, 13). 



