1890.] Entomology. IOI 
the ridges the six longitudinal bands are continued from the colon. 
Passing back the muscles become oblique, and external to the groove 
they are entirely longitudinal. In the cone they are oblique, then cir- 
cular, and near the rectum a few oblique ones again appear. External 
to the muscles is scattered connective tissue. Tracheas and nerve 
fibres enter and ramify in the structure. 
The ridges which compose the cushion are quite marked an teriorly 
and have a central median groove. Posteriorly the ridges are less 
marked, the median grooves becoming as deep as those separating the 
ridges. 
Both from its histology and its position I regard this structure as a 
true rectal gland. Its function, however, I believe to be that of a 
valve. Minot (Histology of the Locust) says that Chun’s decision as 
to their function is only ‘‘a speculative opinion.’ In favor of their 
being valves we find the following facts : 
1. They are the best developed, and the most alike in insects which 
feed on solid and quite innutritious food. In those forms with more 
concentrated or liquid food they vary greatly and may even be want- 
ing. 
2. Their structure is to be best explained by the assumption of a 
valvalar function. This explains the thick spiny chitinous lining and 
the remarkable development of the muscles. 
3. Their location is explained by this assumption, for a valve at this 
point would serve to retain the food in the absorptive portions of the 
digestive track till all nutriment was extracted ; then the combined 
action of the spines and of peristaltis of the muscles would pass the 
remainder on. 
The rectal glands therefore would retain their primitive valvular 
function in those insects which have retained their primitive food 
habits. In the more highly differentiated forms, with concentrated 
food they become modified, serving other purposes or are rudimen- 
tary —H, T. FERNALD. 
EXPLANATION OF FIGURES, PLATES IV. AND V. 
Fic. 1. Longitudinal section of the rectal gland of Passalus, x 50 
(about). C. colon, œ. rectum, ch. chitin layer, cir. m. circular mus- 
cle fibres, cone cone, ¢. £. connective tissue, cush. cushion, ¢. epithe- 
lium, Z m. longitudinal muscle fibres, 2. trachea. 
Fic. 2. Cross section along line A B of Fig. 1 x 90. 
Fic. 3. Cross section along line C D of Fig. 1 x go. 
Fic. 4. Cross section along line Æ F of Fig. 1 x go. 
t 

