494 
MONTGOMERY. 
[Vol. XV. 
I have no material of Piscicola after the breeding season, and 
accordingly could not follow the changes of these gland cells 
in their metamorphosis from the end of the metaphase to the 
commencement of the prophase. But these two end stages do 
not differ much fr^m one another, since the cell at the former 
stage differs from that of the latter merely in that its nucleus 
is smaller and more irregular in shape. 
It is not difficult to determine the sequence of the stages 
described ; only in the smallest individuals do all the stages of 
the prophase occur, and only in the largest those of the 
metaphase. 
20. Mesenchym Cells of Cerebratulus lacteus (Verr.). 
(Plate 29, Figs. 315a, 3^-324.) 
(I have described these cells in a previous contribution (’ 96 ), 
and so shall treat of them in this place mainly with regard to 
their nucleoli.) 
The smallest nuclei (Figs. 316a and 317) are densely filled 
with chromatin, and nucleoli appear to be absent ; the nuclear 
sap also stains with haematoxylin, so that these nuclei may 
be easily recognized by their deep stain and sometimes nearly 
homogeneous appearance. I have made a careful examination 
for nucleoli on preparations stained by the Ehrlich-Biondi 
method, as well as with haematoxylin and eosin, and am 
certain that nucleoli are either wholly absent or, if present, 
must be very minute in point of size. Such, then, is the 
structure of the smallest nuclei, namely, those found in the body 
cavity, and those of the smallest cells of the pseudoepithelia 
lining the body cavity. 
The non-continuous pseudoepithelia of the body cavity are 
layers of differentiated mesenchym cells, which differ from the 
primitive cells in their greater dimensions and more oval or 
spherical outlines (the undifferentiated cells are bipolar or 
multipolar, with long branching processes). In these larger 
cells we find for the first time a spherical, deeply staining 
nucleolus. Now the size of the latter stands in a pretty con- 
stent ratio to that of the nucleus. Further, in the smallest 
