No. 2.] COMPARATIVE CYTOLOGICAL STUDIES. 46 1 



latter, or (and this is the rule for the largest, irregular nucleoli) 

 it is imbedded in the peripheral portion of the nucleolus ; in 

 the former position it is concavo-convex, in the latter, bicon- 

 vex in outline, always being thickest in its median diameter. 

 With the Ehrlich-Biondi staining method it almost invariably 

 colors yellowish, and in only one or two cases did it stain 

 somewhat similarly to the ground substance of the nucleolus ; 

 after fixation in Flemming's fluid, and staining with safranin, 

 gentian violet, and orange G., it always appeared yellowish, 

 while the ground substance remained wholly unstained. The 

 largest nucleoli, i.e., those of the largest germinal vesicles, 

 have always at least one of these bodies in contact with their 

 surface, but quite frequently two may be found on opposite 

 sides of the nucleolus, and in one case I found three (Fig. 277). 

 Those of different nucleoli vary slightly in their dimensions, 

 but my observations give no clue as to their origin. All that 

 can be said of their growth is that in the smaller nucleoli they 

 lie upon the surface of the latter, while they are sunk into the 

 peripheral portion of the larger nucleoli. It differs both chem- 

 ically and structurally from the ground substance of the nucleo- 

 lus, and from the vacuolar substance ; and it would seem to be 

 derived from some part of the nucleus outside of the nucleolus, 

 since it at first lies upon the surface of the nucleolus. This 

 body may be comparable to the " Nebennucleolus " described 

 by Flemming in the &g% of Anodonta ; but I have found no 

 structure in any of the other ova here examined which is 

 identical with it. 



Yolk globules are assimilated by the nucleus from the cyto- 

 plasm, though without the production of amoeboid processes. 

 Such assimilated globules are usually of small size, but some- 

 times large, compound ones are taken into the nucleus (Figs. 

 267-269, 272, 274, 280); they occur most frequently singly or 

 in small masses close to the inner surface of the nuclear mem- 

 brane (Figs. 274 and 280) in almost all of the larger germinal 

 vesicles, and in a few cases some globules may be found near 

 the center of the nucleus. Careful observation shows that the 

 yolk globules really occur within the nucleus, and are not arti- 

 ficially removed there by the knife in sectioning. Usually these 



