322 BULLETIN OF THE 



It is admitted concerning the formation of the daughter nuclei out of 

 the halves of the nuclear plate, that in segmentation spheres the fusion 

 of the plate elements has not been established with certainty. The 

 conclusion is reached, however, that the homogeneous and compacted 

 condition is the original and simplest form in which the nucleus appears, 

 quite contrary to Auerbach's notion of a Jluid cavity in the protoplasm. 

 So, too, the nuclear membrane is not produced from the protoplasm sur- 

 rounding the nucleus, as Auerbach maintains, but, like the nucleolar 

 structures (Binnenkorper), is a differential product of an originally 

 homogeneous corpuscle. In Cucullanus, in Nephelis, and possibly in 

 snails, there are differentiated out of the nuclear plates at first several 

 small nuclei instead of one, each of which afterwards becomes for itself 

 differentiated into a vesicular nucleus, as does in other cases the single 

 nucleus. 



This conclusion arises in part from Butschli's failure to recognize the 

 nature of one of the nuclear structures, the male pronucleus. But 

 aside from that, I have only to say that I have seen nothing of a like 

 nature in the case of Limax. 



Much evidence of similar nliclear conditions is accumulated by Biitschli 

 at pages 409-412, in the course of which he mentions having seen 

 very distinctly in sections through eggs of Rana temporaria the radial 

 structure of the protoplasm around the halves of the " Lebenskeime " 

 (Gotte), when the latter had already advanced into the daughter cells, — 

 a phenomenon which escaped Gotte's attention. 



The more a daughter nucleus grows, the more the central area of the 

 neighboring radial system diminishes, and the former gradually ad- 

 vances to the position of the latter, whence it is to be inferred that the 

 area furnishes the material for the growth of the nucleus ; this consists 

 of fluid, and also of genuine nuclear substance. The nucleus acquires, 

 however, some of this nuclear substance by the retraction of the inter- 

 zonal filaments. When the growth of the daughter nucleus ceases, the 

 central area and the radiation have totally disappeared. 



The want of precision, already noticed, in the account of the time 

 when the segmentation furrow appears, is, if possible, emphasized by 

 the author's saying that the first trace of the division of the yolk appears 

 " somewhere about the time " of the division of the nuclear plate and the 

 separation of its halves, — a period, I should say, of rather indefinite 

 duration, notwithstanding the rapidity with which the halves of the plate 

 begin to move asunder. 



An important role in cell division is to be ascribed, says Biitschli, to 



