MUSEUM OF COMPARATIVE ZOOLOGY. 151 
Among the Metazoa, epithelial tissues offer by far the greatest num- 
ber and the most interesting cases of amitosis. Furthermore, as Ziegler 
C91) has very recently shown, epithelial cells of unusual size, with some 
peculiar functional activity (generally secretion) are most apt to exhibit 
this method of division. Cell division has seldom been observed to fol- 
low amitosis in such large cells, which therefore become multinucleate. 
Other epithelial cells which frequently furnish instances of amitosis are 
those which are near the end of their Functional activity. Cells of the outer 
layer of a stratified epithelium sometimes divide amitotically, while 
those of the deeper (and therefore younger) layers of the same epithelium 
divide by mitosis. A good instance of this was recently described by 
Dogiel (’90) in the epithelium of the bladder of Mammals. The nuclei 
of the large epithelial cells lining the intestine of Arthropods very com- 
monly divide by amitosis, as was found by Frenzel (’85) in the midgut of 
Astacus and Maja ; by Carnoy (’85) in the intestinal epithelium of Iso- 
pods; and by Faussek (’87) in the digestive tract of a Cricket (Hremobia 
muricata) and in the larva of Kschna. The intestinal epithelium in all 
Arthropods has an important secretory function. Cells whose function 
is excretory likewise exhibit amitotic division of the nucleus, as in the 
Malpighian vessels of Insects. ‘The occurrence of amitosis in glandular 
and excretory epithelium is readily explainable on Chun’s hypothesis, 
for the functional activities of such cells are peculiarly intense, and it is 
easy to see that a distribution of nuclear material in the cytoplasm is 
of advantage to the cell. The occurrence of nuclei of unusual size (as 
compared with the nuclei of other cells of the same animal) seems to 
me likewise referable to the peculiar needs of the cytoplasm in these 
cells. 
Cases of amitosis peculiarly difficult of explanation are those pre- 
sented by the germinal epithelium of the testis. So many observers 
have reported direct division in sperm mother-cells, that there seems 
no reasonable doubt of its occurrence. It has been suggested that the 
cells which divide amitotically never produce spermatozoa, but merely 
serve to secrete a fluid. This explanation, however, will not serve in 
the case of certain Isopods (Oniscus asellus and /dotea sp.) in the testes 
of which Carnoy (’85, p. 222) found amitosis the prevailing type of di- 
vision, and mitosis of very rare occurrence. Direct division is found 
more or less frequently in the testicular cells of many other Crustacea, 
as the extensive work of Gilson (’84-87), and the investigations of 
Sabatier (’85) show, and occasionally in the other groups of the Arthro- 
pods. Among Vermes, it was found by Lee (’87) in Nemertians, and 
