144 



FERTFLTZATIOX OF THE OVUM 



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

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

 thus reach the following remarkable conclusion : During cleavage 

 the cytoplasm of tlic blastoinercs is derived from that of the egg, the 

 centrosomcs from the spermatozoon, ivhile the nuclei {cJiromatin) are 



Fig. .73. — Persistence of the centrosomes from cell to cell, in ihc cleavage of the egg of the 

 gephyiean Thalasscina. [GRIFFIN.] 



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

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

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

 figure shown) ; daughter-amphiaster already formed. D. Telophase : the egg dividing and nuclei 

 reforming ; the old amphiaster has disappeared, leaving only the daughter-amphiaster in each cell. 



