No. 2.] COMPARATIVE CYTOLOGICAL STUDIES. 
since the yolk balls increase in size at the beginning of the 
metaphasis, though there appears to be no increase in their 
own ground substance. These unstaining globules are at first 
localized at different points in the yolk ball ; and it would seem 
probable that their substance later mixes itself with the ground 
substance of the yolk ball, since this supposition would account 
for the lessening intensity of the stain of the yolk ball during 
the metaphases. It would appear less probable that these 
globules are metabolic products of the true substance of the 
ball ; however, we have too few facts to enable us to deter¬ 
mine which of these is the correct view. 
Certain curious structures found in the cytoplasm of an 
immature worm fixed with Lang’s fluid (aqueous corrosive 
sublimate solution, NaCl, acetic acid) may be mentioned here. 
In the cytoplasm of a number of ova, in none of which any 
yolk was present, I found a few small, ring-shaped bodies, 
which stained with haematoxylin much more intensely than 
the surrounding cytoplasm ( Yk . Bl.f Fig. 233). Each con¬ 
sisted of a ring composed of a dense, homogeneous substance, 
the inner surface of the ring being smooth, but the outer irregu¬ 
larly jagged, this whole ring (as it appears on a section) enclos¬ 
ing an unstaining vacuole or globule. In reality these bodies 
are spheres, but my description applies to sections of them. 
These structures vary considerably in size, and sometimes are 
not spherical but oval, the larger ones usually staining more 
deeply than the smaller ones. I found them only in some of 
the ova of this one individual, and nothing of the kind was to 
be seen in the ova of about twenty other individuals sectioned, 
which had been variously preserved in picric, osmic, and chromic 
acids, in simple aqueous solution of corrosive sublimate, and in 
the fluids of Hermann and Flemming. Accordingly, they must 
be regarded as artefacts, produced by the action of the acetic 
acid, which I have long since found to be a very unreliable fixa¬ 
tive for the cytoplasmic elements of the nemerteans. It is 
most probable that they are young yolk balls, to which the 
acetic acid has given an abnormal appearance. Or might they 
represent multiple asters, such as have been recently described 
by Mead in Chaetopterus ? 
