No. 2.] COMPARATIVE CYTOLOGICAL STUDIES. 491 



return to the chemical change later); in other words, the sub- 

 stance of those nucleoli which have come to be situated in the 

 cell body undergoes a physical and perhaps a chemical change 

 in this portion of the cell, and their expansion in volume might 

 be accounted for on the ground of there being a smaller degree 

 of pressure in the cell body than there is in the nucleus. 



It will be noticed that the prophase and the metaphase of 

 the cell body and of the nucleus do not exactly coincide in 

 point of time, the metaphase of the nucleus commencing earlier 

 than that of the cell body. Thus the nucleus attains its great- 

 est dimensions and most diverse ramification at the time when 

 the cell body contains the greatest amount of homogeneous 

 substance, and the nucleus enters on its metaphase (diminu- 

 tion in volume, retraction of processes, expulsion of nucleoli) 

 when the secretion corpuscles are only commencing to arise in 

 the cell body. At the beginning of the metaphase of the cell 

 body (when the latter is filled with the secretion corpuscles and 

 commences to excrete them) the nucleus has already assumed 

 a nearly spherical or oval form, has greatly decreased in size, 

 and has discharged most of its nucleoli into the cell, i.e., the 

 nucleus has advanced already some distance in the path of 

 the metaphasis. 



The metaphase of the cell body (Figs. 198-203) commences 

 when the cell is filled with the secretion corpuscles, all traces 

 of the previous homogeneous substance being absent, and begins 

 to discharge them through its duct. During this process the 

 cell gradually decreases in size, and the primitive cytoplasm 

 again comes into view, at first in the form of delicate fibers. 

 When the cell has shrunk to about one-third of its former size 

 (the diameter of the duct does not decrease quite so rapidly, 

 since it may be still full of secretion corpuscles after they have 

 all disappeared from the cell body) the nucleus has simultane- 

 ously decreased in size, but with greater proportionate rapidity 

 than the cell body, and so at the close of the metaphase (Fig. 

 202) the nucleus reaches its smallest relative size. The latter 

 contains at this stage invariably a single nucleolus, of spherical 

 or oval form, very regular in outline, and exactly similar to the 

 nucleolus at the commencement of the anaphase except that 



