144 



FERTILIZATION OF THE OVUM 



continuity is not broken in later stages. An exactly similar process 

 is described by Kostanecki and Wierzejski in the egg of PJiysa. We 

 thus reach the following remarkable conclusion : During cleavage 

 the cvtoplasm of the blastouieres is derived from that of the egg, the 

 centrosomes from tJic spermatozoon, while the nuclei (clirornatin} arc 



B 



Fig- 73- Persistence of the centrosomes from cell to cell, in the cleavage of the egg of the 

 gephyrean Thalasseina. [GRIFFIN.] 



A. Mitotic figure for the first cleavage ; the centrosome already double in each centrosphere 

 (the small black bodies are deutoplasnt-spheres). B. Early anaphasc ; migration of the centro- 

 somes to the periphery of the centrosphere. C. Middle anaphase (only one-half of the mitotic 

 figure shown) ; daughter-amphiaMer already formed. /). Telophase ; the egg dividing and nuclei 

 i '-forming ; the old amphiaster lias disappeared, leaving onlv the daughter-amphiaster in each cell. 



