No. 2.] COMPARATIVE CYTOLOGICAL STUDIES. 461 
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 egg 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 
