MUSEUM OF COMPARATIVE ZOOLOGY. 559 



possibly be accounted for by the more or less advanced condition of the spindle 

 formation. The same differences in the degree of advancement may also ex- 

 plain why Mayzel did not meet with the nuclear plate composed of granules of 

 a more uniform size. The conditions he has described I have also seen ; but I 

 have besides that seen other conditions which do not warrant the conclusion 

 that the spindle fibres remain like the astral rays, even though they may still 

 be called smooth filaments. 



There is one point especially in which my own observations have not the 

 clearness I should desire. I have not been able to remove all doubt about the 

 confluence of the lateral zones of fibre thickenings into a homogeneous nucleus. 

 It has been difficult to exclude the possibility that in some cases the granulations 

 may persist to form the nucleoli. Unfortunately, the 'observations of Mayzel 

 do not serve to make the matter any more certain. He says : " Die aus 10-15 

 Kleinen, hellen ovalen und rundlichen kernahnlichen Gebilden bestehenden 

 ' Kernhaufen,' welche ich im Sinne Biitschli's als zusammenfliessende deuten 

 mochte, erscheinen bei der Isolation wie von einer gemzmschaftlichen Memhran 

 umgeheny I am unable to reach an entirely satisfactory conclusion as to the 

 nature of the bodies thus described by Mayzel. If, as the author thinks, 

 they are identical with Biitschli's "cluster of nuclei," the signification of the sur- 

 rounding membrane is not apparent. Biitschli has described no such structure, 

 and each of his " Kernchen," moreover, contains one or more nucleolar bodies. 

 These Mayzel does not mention, and I have never seen in Limax anything cor- 

 responding to this condition. It therefore appears more probable that the de- 

 scription given by Mayzel relates to a subsequent stage, — to one at least as late 

 as that shown in Fig. 93, — and that his nuclear bodies are really nucleoli. 

 But the homogeneous condition of the nucleus, if it exists at all, precedes this 

 stage. It is certainly an objection to the view I have suggested that the author 

 looks upon these nucleus-like structures as in process of fusion. That cannot 

 be claimed, I think, for the 8-10 small structures shown in Fig. 93, vsince my 

 preparations show a constant increase in their number accompanying the in- 

 crease in the size of the nucleus. I find, then, no sufficient grounds in May- 

 zel's observations for changing the opinion previously expressed, that the 

 thickenings of the lateral zones fuse into a single homogeneous nucleus at an 

 early stage, namely, before the differentiation of nucleoli. 



The researches of Perez ('79) on presegmentation stages in Helix aspera 

 possess the merit of covering the very early conditions of the egg, — the 

 changes which transpire while it is still in the " diverticulum" and the ovi- 

 duct, — but the general conclusions at which he arrives do not appear to me 

 to offer so satisfactory an explanation of the phenomena as the more generally 

 received opinion.* 



* Perez alludes to the eggs of Liraax agi-estis, simply to call attention to the fact 

 that when immersed in water the shell becomes distended by the accumulation of 

 water between it and the membrane of the albumen. This, he says, may perhaps 

 explain why Van Beneden held that there was a special liquid between these two 

 layers. 



