284 



piece into a large number of deeply staining granules (Dia. C, D). 

 No sperm centrosome or amphiaster is present at any time during 

 the movement of the sperm through the egg and no astral radiations 

 appear in connection with the sperm until the anaphase of the second 

 maturation (Dia. D). At this time radiations appear around the 

 granules from the middle piece; the central area of this aster grows 

 rapidly and is filled with coarse granules. This is the sperm sphere 

 and it develops pari passu with the egg sphere, which it resembles 

 in every particular (Dia. E). Each sphere remains in contact with 

 its nucleus and when the germ nuclei have come into contact the egg 

 and sperm spheres fuse into a granular mass which partially surrounds 

 the germ nuclei. Within these fused spheres the two cleavage centro- 

 somes arise (Dia. F). They are at first quite independent of each 



FblarBodl 



Egg N^A.clevA.s 



J f tiers 



Cleavage Cei\tT05omcr 



E 



Diagram E. Approacli of germ nuclei and spheres. 



Diagram F. Union of germ nuclei and spheres. Appearance of cleavage cen- 

 trosomes. 



other and one is always in contact with each of the germ nuclei 

 (Dia. F, G). After some time a central spindle appears between the 

 two centrosomes and the first cleavage is introduced (Dia. H). 



There is no "quadrille" of the spheres, or asters, as maintained 

 in my first paper i) on this subject, the appearance of a division of 

 the spheres and their subsequent fusion by pairs which I formerly 



1894. 



1) CoNKLiN, The Fertilization of the Ovum. Woods Holl Lectures, 



