50 Wisconsin Academy of Sciences, Arts and Letters . 
thin chitinous intima into the lumen of the pyloric valve. The 
circular muscles are greatly developed, and, according to Van 
Gehuchten, “peuvent etre consideres com me un appareil d’oc- 
clusion, destine a empecher les matieres alimentaires, soit do 
passer trop vite dans Tintestine terminal, soit de revenir du 
gros intestine dans le ventricule chyiifique.” 
A transverse section through the pyloric valve shows that the 
epithelial layer, which is lined with a chitinous intima, is 
thrown into a number of broad folds (15 to 18). The epithe¬ 
lial cells of these folds are little longer than broad, while in the 
space between the folds they are more flattened. The long axis 
of the ovoid nuclei is usually at right angles to the chitinous 
intima. External to the thick circular muscles are the longi¬ 
tudinal, which can be traced from the mid-intestine, between 
the Malpighian tubules, over to the ileum. These are covered 
externally by the peritoneal membrane. 
Posterior to the pyloric valve, the folds of the ileum become 
less numerous and very irregular in shape. The conical spines 
which project from the chitinous intima into the lumen of the 
pyloric valve are replaced by blunt projections. The cells con¬ 
tain a slightly granular cytoplasm, which, in places, shows a 
distinct longitudinal striation. The nucleus, usually ovoid 
in shape, takes up the larger part of the cell (Pig. 12). The 
circular muscles, after their temporary thickening at the py* 
loric valve, pass over into a thin layer. Erom the external 
longitudinal muscles, branches are given off which enter the 
folds of the ileum and attach to the chitinous intima. The 
longitudinal muscles are covered by a thin, delicate peritoneal 
membrane. 
The ileum is invaginated into the rectum, as is shown in a 
longitudinal section through these two parts (Fig. 15, il). At 
this region, the ileum attains a somewhat better development 
of the circular muscles, and the folds almost fill up the entire 
lumen. Evidently this great development of the circular mus¬ 
cles serves, when they contract, to retain the nourishment with¬ 
in the ileum. According to FTewport (20), the ileum of Athalia 
centifoliae also ends in a valve. We propose to call this valve 
the posterior iliac valve , to distinguish it from the pyloric valve 
