No. 2.] COMPARATIVE CYTOLOGICAL STUDIES. 
and material which has been more advantageously fixed and 
stained. 1 
io. Poly dor a. 
(Plate 28, Figs. 249-281.) 
The egg cells of this form, as those of most Polychaeta , are 
derived from the peritoneal cells of the body cavity, the latter 
cells building pseudoepithelia around the intestine, as well as 
occurring free in the body cavity. Those in the pseudoepi¬ 
thelia (Fig. 249) are more or less flattened, disc-shaped, while 
the free cells (Figs. 250-254) are oval in shape, with more 
regular outlines. Their cytoplasm is not dense, and one or several 
large vacuoles are frequently found at the periphery of the cell; 
a delicate cell membrane is present. The cytoplasm of these 
sexually indifferent cells does not stain with haematoxylin. The 
nucleus is small, irregular in outline, and contains a few chromatin 
granules ; very frequently the greater part of this substance lies 
close to the nuclear membrane. I have never found more than 
one minute nucleolus, and this is almost always close to, or in 
actual contact with, the nuclear membrane (Figs. 251, 252, 254); 
in many nuclei I failed to find nucleoli, though in these cases they 
may have been obscured by the chromatin. I found one divi¬ 
sion stage of a nucleus (Fig. 249) ; there were two daughter- 
nuclei of the same size and form lying close together ; the 
nucleolus of each was somewhat elongate in form (in all others of 
these cells examined it is spherical), which might show that the 
nucleoli had been produced by the division of a single one in the 
mother-nucleus. In many of the smaller free peritoneal cells 
a peculiar body often occurs (N. P. Fig. 253). This is always 
smaller than the nucleus, more or less spherical, often homo¬ 
geneous in appearance, and it may stain either deeply red with 
eosin or faintly with haematoxylin, or in other cases it may not 
stain at all, but appear as a light yellowish, refractive mass. 
From the comparative study of a large number of cells contain¬ 
ing these bodies it may be determined that they are degener¬ 
ated nuclei or portions of nuclei. Thus in Fig. 250, which 
1 For other observations on nucleoli of Siphonophora , cf , besides the paper by 
Conklin and Brooks, the review of O. Hertwig (’ 78 b). 
