218 REPORT UNITED STATES ENTOMOLOGICAL COMMISSION. 
and, like that on the ileum, it rests upon a layer of connective tissue, 
beyond which follows (1) an internal coat of longitudinal, and (2) an ex- 
ternal coat of circular muscular fibres, which are striated. 
Rectum. — The rectum of insects is remarkable for containing certain 
curious structures now generally known as rectal glands. They are in- 
cidentally mentioned by older authors, but Frey and Leuckart 309 were, as 
far as I am aware, the first to recognize their general distribution and 
importance. Leydig 310 was the first to give an accurate account of their 
histological structure. Since then they have received but little atten- 
tion until 1870, when Dr. Chun published his investigations, 3 " which were 
made under the guidance of Professor Leuckart. Chun extended his 
researches over a variety of insects, but gives no account of the glands 
as found in the grasshoppers, though he studied the closely allied Katy- 
did (Locusta viridissima, I. c., p. 32). He describes the glands as six flat 
folds, formed by a high epithelium and well-defined cuticula; the con- 
nective tissue (tunica propria) is largely predominant ; there is a coat of 
circular muscular fibers, and six external longitudinal muscular bands, 
corresponding to the furrows between the glands. This description is 
applicable also to the grasshoppers I have investigated, the oidy differ- 
ences being in the structural details of the single layers. 
Seen from the inner surface the epithelium presents a most curious 
and puzzling aspect, Fig. 53, because there are two kinds of nuclei 
at different levels; small, spherical nuclei nearest the surface, and 
larger nuclei of oval form deeper down. The small nuclei are less 
numerous than the large ; in the portion represented in Fig. 48 there 
are 21 small aud 49 large nuclei, or, in other words, less than half as 
many of the superficial as of the deep nuclei. As the two sets are at 
different levels they cannot both be in focus at once, hence in drawing 
Fig. 53 with the cameraducida, the large nuclei were first focused 
and drawn, and then the smaller nuclei were drawn in the same way 
over the first. When we focus upon the large nuclei, the polygonal 
outbines of the cells can be seen in successful preparations as repre- 
sented in the figure ; as there are no spaces between the cells with the 
large nuclei, the cells belonging to the small nuclei do not extend so far 
down, though the cells of the large nuclei do reach up among the small 
nuclei, as can be seen in sections. The outlines of the cells to which the 
small nuclei belong, I have not been able to distinguish. 
The small nuclei are spherical, very refringent, and have a sharp out- 
line. The large nuclei are oval, their long axes lying generally length- 
wise rather than transversely on the folds of the rectum. An epithelium 
presenting a somewhat analogous peculiarity has been described from 
the epididymis of mammals by Klein. 312 He figures small darkly stained 
309 Frey and Leuckart: TTebersicht des Thierreichs, 1855, p. 11G. 
3W Leydig : Lehrbuch der Histologie, p. 337. 
311 O. Ohun: TJeber den Bau, die Entwickelung und physiologische Bedeutung der Rectaldriisen be! 
den Insecten. Abh. : Senckb. Natforsch. Ges. (Frankfort) Bd. x, p. 27, mit drei Tafeln. 
312 Klein: Observations on the structure of cells and nuclei. Quart. Journ. Micros. Sci., XLX, (1870), 
p. 138, pi. VII, fig. 9. 
