320 



SOME PROBLEMS OF CELL-ORGANIZATION 



The amphiastral formation in alveolar protoplasm gives very clear 

 evidence against the theory of fibrillar persistence. Here the fibrillar 

 rays can be seen growing out through the walls of the alveoli ^ quite 

 distinct from, though embedded in, them. At the close of mitosis 

 every trace of the fibrillar formation may disappear, e.g. in echino- 

 derm-eggs after formation of the polar bodies, the protoplasm retain- 

 ing only a typical alveolar structure. 



Fig. 155. — Stages in the first cleavage of the egg in Cerebratubis {A-C, COE) and Thalassema 

 {D-F, Griffin). 



A. First appearance of the cleavage-centrosome at the poles of the fused germ-nuclei ; cleavage- 

 asters forming within the degenerating sperm-asters. B. Final anaphase of first cleavage, showing 

 persistent centrosomes and new asters forming. C. Immediately after division. D-F. Three 

 stages of the late anaphase in Thalassema, showing formation of new asters within the old. {Cf. 

 Fig. 99.) 



The strongest evidence against fibrillar persistence is, however, 

 given by recent studies on mitosis, showing on the one hand that the 

 new astral centres do not coincide with the old ones, on the other 

 that the old rays degenerate /// siiu, to be replaced by new ones. 

 Aside from many earlier observers, who believed the entire aster to 

 disappear at the close of mitosis, the first to assert the wholly noJv 



1 Cf. Reinke ('95), Wilson ('99). 



