The area of new cell formation, the rate of proliferation, and the manner in which cells are lost from the intestinal epithelium in the turtle, Chrysemys picta, were studied using a cell labeling technique with tritiated thymidine and mitotic inhibiting technique with colchicine.
In the intestinal epithelium of Chrysemys picta, cellular proliferation was observed to occur in the layer of cells adjacent to the basement membrane. Mitosis occurred throughout the epithelium at a fairly low rate (mitotic index 0.0016). In the upper intestine fewer labeled cells were found in the apical one-third of a villusfold than in either the mid or basal one-third. The time required to renew the intestinal epithelium, was estimated to be about eight weeks in winter turtles maintained at 20° to 24°C.
Cell loss from the system appeared to be due to a randomly located movement of cells lumenward from the basement membrane.
Mitotic activity in cold torpid turtles (11°C ambient temperature) appeared to be completely suppressed as shown by a lack of incorporation of tritiated thymidine and an absence of mitotic figures in the intestinal epithelium.
The term villi-folds was proposed to provide a category for those animals possessing structures having characteristics both of villi and of folds as found in C. picta.