750 CALKINS. [Vol. XV. 



the homogeneous portion. Balbiani agrees with neither. He 

 thinks that the " nucleolus " which is found in the granular 

 part of the nucleus is not an initial but a final step in division 

 (telophase), the corpuscle or "nucleolus " forming as follows : 

 The ends of all the chromatin filaments converge at the pole 

 during the telophase. These ends, which at first are closely 

 pressed together, separate later, and a space or vacuole is made 

 containing several granules. The latter collect together at a 

 later stage to form a single corpuscle. This corpuscle is the 

 " nucleolus," and from here it passes through the granular and 

 into the homogeneous part of the nucleus, where it undergoes 

 the changes so carefully described by both Hertwig and 

 Balbiani. 



The peculiar changes which this corpuscle undergoes led 

 Balbiani to regard it, quite independently of the " pole-plates," 

 as the " centrosome." 



He says: " Le globule central participe k la fois des caracteres d'un 

 nucleole vrai, et d'un centrosome; comme nucleole, il disparait par resorption 

 dans la substance achromatique au debut de la division, pour se regenerer 

 chez les deux nouveux noyaux par les processus indiqud plus haut; comme 

 centrosome il condense autour de lui la substance environnante son forme 

 d'une petite sphere attractive intra-nucleaire, que ne passe pas du noyau 

 dans le protoplasma pour y jouer le rSle d'un centrosome ordinaire pendant 

 la division de la cellule " (p. 309). He denies Hertwig's homology of " end 

 plates " to " Polkorperchen " or centrosomes, because they are nuclear in 

 origin, whereas the latter are cytoplasmic, and he attempts to explain them 

 "comme des accumulations, aux deux poles du noyau en division, de sa 

 substance achromatique, et leur destinde est de ramener les noyaux nouveaux, 

 au type normal du noyau au repos chez le Spirochone " — which explains 

 nothing at all. 



From Balbiani's description of the " achromatic " parts in 

 Spirochona it is evident that this nucleus presents one achro- 

 matic element separated from the chromatin by a " fente," and 

 similar to the sphere in Noctiluca; and a second element, — the 

 so-called "centrosome " — which is derived from the chromatic 

 portion of the nucleus. This body passes from the chromatin 

 into the "achromatic" part of the nucleus, possibly in the same 

 manner as the centrosome in Noctiluca is supposed to pass 

 from the nucleus into the sphere. It cannot be identified with 



