Severin and Severin—Anatomical Studies of Cimbex. 41 
cause they are inserted posterior to the constriction. We find 
in Cimbex americana also a Tenthredinida, that the Malpigh¬ 
ian tubules enter the mid-intestine at a region anterior to the 
constriction (Fig. 13, mlp). 
The next division of the alimentary canal, the hind-intes¬ 
tine, is clearly separable into an anterior convoluted portion, 
the ileum (Tig. 2, it), and a smooth, thicker posterior part, 
the rectum (Fig. 2, r). The ileum is bent once or twice upon 
itself; the rectum passes as a straight tube through the rest of 
the abdomen. On the wall of the rectum, and lying parallel 
with it, are six white elliptical thickenings, the rectal glands 
(Fig. 2, rg ). Three of these are situated a little anterior to 
the other three, which alternate with them. 
Histological Structure of the Alimentary Canal. 
FORE-INTESTINE. 
Oesophagus :—A study of a series of cross sections through 
the oesophagus shows that at the beginning of this part of the 
fore-intestine there are a large dorsal and a few smaller lateral 
and ventral folds (Fig. 4). Passing backward, this large dor¬ 
sal fold decreases gradually in size, but as it becomes smaller, 
the lateral and ventral ones become more numerous. In the 
posterior head region the dorsal fold cannot be distinguished, 
but here the folds are very irregular in shape and almost fill 
the lumen. Internally, the lumen is bounded by a hyaline 
chitinous intima, which is thickest immediately posterior to 
the pharynx. Throughout the rest of the oesophagus it varies 
but little in thickness. The chitinous intima rests upon an 
epithelial layer which, at the anterior end of the oesophagus, 
is represented by cells with cell boundaries usually indiscern¬ 
ible. Here and there between these epithelial cells are mul- 
tinucleated glands, which are usually found within the folds 
(Fig. 4, gla). The nuclei of these glands are larger than 
those of the epithelium. Usually one or more canals can be 
traced from these glands, passing through the chitinous intima 
and opening into the lumen of the oesophagus (Fig. 4, pc). 
In the posterior head region and throughout the rest of the 
