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 from 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, 3163-324.) 



(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- 

 stant ratio to that of the nucleus. Further, in the smallest 



