100 The American Naturalist. (January, 
ENTOMOLOGY .! 
Rectal Glands in Coleoptera.—While studying the histology of 
Passalus coenutus Fab., recently, I found in the alimentary canal, be- 
tween the colon and rectum, a structure which I consider homologous 
with the similarly located rectal glands of other groups of insects. 
The colon has six longitudinal rows of diverticula, each diverticu- 
lum being in depth about one-third of the diameter of the colon. It 
consists of a somewhat spiny chitinous layer. Next is the lumen, ex- 
ternal to which is a layer of cubical epithelial cells. Next is a layer 
of circular muscle fibus, and, alternating with the six rows of diver- 
ticula, six bands of longitudinal muscle fibres. 
The rectum has a lining of smooth chitin resting on an epithetial 
layer, the cells of which are slightly more calumnar than those of the 
colon or of the intervening structure. Then come scattered circular 
muscles and six bundles of longitudinal fibres. 
The anterior end of the structure uniting the colon and rectum forms 
the posterior wall of the last diverticulum of each row. Rising towatds 
the lumen proper, from the bottom of this diverticulum, the wall soon 
bends posteriorly, forming a sort of side pocket, then returns and 
completes the posterior side of the diverticulum. The wall now passes 
backward for a distance about equal to that of three diverticula, then 
turns outward and slightly forward forming a small groove around the 
tube. It then bends back, narrowing the diameter of the lumen and 
making this rather conical, then gradually widens and becomes modi- 
fied to form the rectum. 
The anterior of these two parts of the structure I shall term the 
cushion, and the posterior portion, the cone. In cross-section the 
cushion is seen to consist of six longitudinal ridges, each ridge con- 
tinuing the line of a row of the diverticula of the colon. The chitin 
in the last of these is smooth, but when it bends and forms the inner 
face of the cushion it becomes thickly set with short blunt spines, 
which point backwards. There are no spines in the groove between 
the cushion and the cone, but they begin at the posterior edge of the 
groove, and continue from this point to the rectum. 
In both cushion and cone the underlying epithelium is cubical and 
contains prominent nuclei. It shows no traces of a glandular func- 
tion. 
The muscles are greatly developed. At the anterior end of the 
cushion they pass from one side of a ridge to the other, and between 
1 This department is edited by Prof, J. H. Comstock, Cornell University, Ithaca, N. 
Y., to whom communications, for notice, etc., should be sent. 


