190 PROCEEDINGS: BOSTON SOCIETY NATURAL HISTORY. 
and regenerative processes which run the same course in all parts 
of both regions, but could only be studied in detail for the ileum. 
The metamorphosis of the colon is very peculiar. 
According to Hurst (’ 96 ) the epithelium of the intestine “divides 
into a thin outer and a thick inner layer. The latter becomes loos¬ 
ened, breaks up and appears to be digested.” The process for the 
species of Culex that I studied is not as simple as this would imply. 
The battened epithelium first becomes columnar. Then the cells 
degenerate, separating more or less from one another. Large vacu¬ 
oles make their appearance, the cytoplasm becomes spongy, and a 
small amount of debris , in which granules of chromatic material are 
noticeable, is given off into the lumen of the canal. In all regions 
considerable mitosis was observed toward the end of the changes. 
The processes begin at the upper end of the ileum, run their course 
here in about six hours and then involve simultaneously the rest of 
the ileum and the rectum, lasting eight or ten hours. They result 
in the formation of an epithelium of small, dark-staining cells, some¬ 
what like the cells of the new anal ring. These gradually alter to 
the adult characters for each region. Enlargement and probably 
proliferation of cells in certain parts of the rectal walls form the 
rectal papillae (pi. 17, fig. 53, p). The muscle-coats are lost about 
the seventeenth hour and are later replaced by new muscles. 
It is evident that in the metamorphosis of the ileum and rectum 
certain of the epithelial cells are eliminated and new cells, derived 
from epithelium which escapes destruction, replace them. Probably 
the degenerative process involves all the older cells to a greater or 
less degree. The nuclei of the reconstructed epithelium are barely 
one half the size of the nuclei of the older cells. The nature of the 
preliminary alteration by which the epithelium becomes columnar 
is obscure. It does not seem, however, to depend on any contrac¬ 
tion of the walls of the gut. 
The alterations recorded above are not without relation to the 
postembryonic development of the hind gut in such flies as Musca 
or Gastrophilus. In the latter genus, the hind gut is destroyed and 
is reconstructed from an anterior imaginal ring of regenerative cells 
near the Malpighian tubules and a posterior ring near the anus 
(Vaney, : 02). The hind gut of Musca evidently undergoes a simi¬ 
lar metamorphosis, but observers do not agree as to the amount of 
epithelium destroyed. Kowalevsky (’ 87 ) asserts that all the older 
