PRELIMLYAKY GENERAL SKETCH 



195 



cleavage before the first cleavage takes place. The minute centro- 

 somes of the second cleavage are therefore the direct descendants of 

 the sperm-centrosome ; and there is good reason to believe that the 

 continuity is not broken in later stages. The facts are nearly similar 









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A 



• • • 



»•?••• v.. 



* • •• 



.e • 



• ••^ 



"-^^ 





B •' 



,^- ♦ •' 



• «.; 





\ 



c 



/ 



/ 



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 * • 





/ 



A 



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Fig. 99. — Fertilization in an annelid (armed Gephyrean), Thalasscma. [CiRlFFlN.] 



A. Second polar body forming; sperm-nucleus and centrosome below. />. Apjiroach of the 

 egg-nucleus and sperm-nucleus, the latter accompanied by the sperm-amphiaster. C. Union of 

 the nuclei. D. Later stage of last. E. Prophase of cleavage-spindle. /'. Anaphasr of the same; 

 centrosome divided. G. H. I. Successive stages in the nuclear reconstitution and lormation of 

 the daughter-amphiasters for the second cleavage. J. Two-cell stage. 



in the trout, in Chcetoptcrus, and in PJiysa. In Ascaris division of 

 the centrosome first occurs at a somewhat later period ( Figs. 90, 176). 

 If now the centrosomes were indeed permanent cell-organs, wc 

 should thus reach the following result: During cleavage the cytoplasm 

 of the blastomeres is derived from that of the egg, the centrosomes from 



