478 MONTGOMERY. [Vol. XV. 



series of divisions from the single original one. This division 

 usually commences, then, when the form of the nucleus changes 

 from the original oval to a more elongate shape. It seems 

 probable that this elongation of the nucleus may directly cause 

 the division of the nucleolus, since the long axis of the latter 

 coincides with that of the nucleus ; and were the nucleolus in 

 any way fixed in position in the nucleus, the nuclear elongation 

 would draw out the nucleolus and cause it to break into frag- 

 ments. But the division of the daughter-nucleoli does not 

 always take place in the direction of the long axis of the 

 nucleus, so that some other factor might be at work to produce 

 this division. 



The chromatin is arranged in the form of a reticulation (Fig. 

 326). The nuclei of the younger cells are usually regular in 

 outline, but those of the larger ones become very irregular ; 

 this irregularity of the contours of the nuclei is more marked 

 by fixation with corrosive sublimate than with Flemming's fluid, 

 so that it might be regarded as an artefact caused, e.g., by the 

 obstacle offered to the rapid penetration of the preserving 

 fluid by the dense outer (fibrillar) layer of the cytoplasm in 

 the largest muscle cells. 



17. Blood Corpuscles of Data. 

 (Plate 22, Figs. 9S-101 ; Plate 23, Fig. 102.) 



(These cells are usually to be found abundantly in the 

 cavity of the cirratida and of the sheaths of the tentacles, 

 though their number varies greatly in different cirratida. 

 They lie in the meshes of the loose network of mesenchym 

 cells, either singly or grouped together into bundles. I have 

 been unable to find them in other parts of the body. These 

 cells appear to be free mesenchym cells, with perhaps the 

 function of blood corpuscles.) 



There is always a single large nucleolus, which is usually 

 very large in proportion to the size of the nucleus. It varies 

 in form from a perfect sphere to an elongate oval. The nucleo- 

 lar substance is usually homogeneous, but in some cases it is 

 granular (Figs. 99-102) and then it stains faintly as if it were 



