38 University of California Puhlications in Zoology [Vol. 11 



deeply, the cytoplasm becomes pale and less granular; being 

 vacuolated in many cells, the cell walls become less well marked 

 and finally disappear so that the central portion of the nest is 

 a necrotic mass of indistinct cell elements. In the same order, 

 the nuclei are also enlarged, become increasingly vacuolated, con- 

 tain bizarre clumps of chromatin, stain faintly, the limiting 

 membrane becomes le.ss well defined and finally disappears en- 

 tirely so that they (the nuclei) are no longer vi.sible. 



Cell Inclusion. — Beside the normal cell contents nearly all 

 of the epithelial cells contain the cell inclusion mentioned above. 

 This cell inclusion which occurs so constantly in the epithelial 

 cells, has been thought by many to be analogous to the cell in- 

 clusion present in carcinomata and by others to the inclusion seen 

 in the lesions of variola, vaccina, etc. Reischauer (1906) and 

 others have taken it to be an animal parasite, while Burnet 

 (1906), Apolant (1902), and many others thought it to be merely 

 a i^roduct of cell degeneration. 



Form and Occurrence in Cells. — The cell inclusion is sphe- 

 roidal or ellipsoidal, u.sually larger than the nucleus, has fairly 

 definite boundaries, although we were not able to see a definite 

 limiting membrane. It lies in the neighborhood of the nucleus. 

 U.sually a single one is found in each cell, the exceptions to this 

 being, first, at times two of these bodies are seen in a single cell ; 

 and second, some enlarged cells do not appear to contain any. 

 However, this apparent absence of a cell inclusion is probably 

 due to the inclusion lying outside the plane of the section in 

 the enlarged epithelial cell. Rarely these bodies are seen in inter- 

 cellular spaces. Apparently these cell inclusions are not present 

 in the epithelial cells which are in process of active proliferation. 

 However, this is a difficult point to determine accurately, because 

 there are cells containing the cell inclusion which lie within the 

 proliferating zone and which do not shown any signs of degenera- 

 tion. Although these cells do not show any signs of degeneration, 

 only those which do not contain the cell inclusion show evidence 

 of normal active proliferation. At times cells containing the cell 

 inclusion also contain atypical mitotic figures, but on the whole, 

 it seems fairly certain that the appearance of the inclusion in 

 a cell accompanies a cessation of proliferation. 



