EARLY DEVELOPMENT OF GRANTIA COMPRESSA. 291 



3. The entry o£ the spermatozoon into the collar-cell does not cause the 

 former to break up into its constituent parts. 



4. The entry of the sperm into the collar-cell or choanocyte causes the 

 latter to lose its collar and flagellum. Subsequently the nucleus of the 

 collar-cell may lose that characteristic smooth chromophil baekoround, and 

 become more open and reticulate — this does not always occur. The sperm- 

 containing choanocyte sinks below its fellows in the epithelium (text-fig. 3), 

 passes through the basement-membrane of the choanocyte epithelium, and 

 comes to rest on that surface of the oocyte nearest the collar-epithelium. 

 Occasionally, the sperm-bearing cell makes a hollow in the egg, into which 

 it fits (PI. 20. fig. 11). 



5. The wall of the sperm-carrying cell and of the oocyte vitelline membrane 

 come into direct contact ; they become interrupted, protoplasmic continuity 

 is established, and the spermatozoon flows passively into the egg (PI. 20. 

 figs. 11, 12, 14, and 16). 



6. The sperm may enter the egg frontways, backways, or sideways (PI. 20. 

 figs. 11 and 12). 



7. The sperm does not appear to undergo the special rotation noted in 

 other forms. 



8. The sperm-carrying cell, after the sperm has passed away, does not 

 immediately change, for it can be found during earlj- cleavage. Later on it 

 becomes increasingly difficult to find this cell, and one is led to believe that 

 it subsequently wanders away from the scene of its former activity. In one 

 case I thought the sperm-carrying cell had begun to degenerate. 



9. From the fact that the spermatozoa are always found in a circumscribed 

 area of the flagellated cavities, just where the eggs lie, it has been concluded 

 that this is a definite example of chemotaxis (text-fig. 4). 



Fertilization (2nd Part). 



10. The spermatozoon, after entry into the egg, first of all loses its cell- 

 wall, which degenerates. 



11. The acrosome next becomes chromophobe, while the edoes of the 

 sperm-cytoplasm tend to spread into the surrounding egg-cytoplasm, beino- 

 for some time recognizable by its coarse stringy appearance, but later it can 

 no longer be noticed (PL 20. figs. 16 and 17). 



12. The sperm nucleus now begins to grow, and other nucleoli put in an 

 appearance (PL 20. fig. 13). The nucleus becomes spherical. 



13. The sperm-middle-piece or macromitosome breaks up into a cloud of 

 fine granules, which adhere to the growing male-pronucleus like the tail of a 

 comet (PL 20. fig. 17, MAM). In a later stage these granules could not be 

 identified. 



14. Soon after the entry of the sperm, one finds that in the majority of 

 oocytes there is a flowing towards the region of entry of many of the 



