STRUCTURE OF THE GASTRIC CCECA. 
215 
whose observations are also cited by Leydig on p. 337 of his "Hand- 
buch." Sirodot 305 repeats the old and incorrect statement, while Graber 306 
expressly states that their structure is not the same as that of the stoin- 
acb, and that they are not " einfache Aussackungen des Chylusinagens." 
More recently M. F. Plateau 30 " has again called attention to the incorrect- 
ness of the old view. 
In fact, a single transverse section of one of the diverticula (Fig. 37) 
demonstrates at once that its structure is entirely different from that of 
the stomach. Its inner surface is thrown up into longitudinal folds, 
generally twelve in number. These folds shine through the outer walls, 
and are, accordingly, indicated in the drawings of Dufour, Graber, and 
others. The whole diverticulum has an external muscular envelope, out- 
•side of which are a few isolated longitudinal muscular bands. The 
folds within are formed mainly by the high cylindrical epithelium, which 
lines the whole interior of the cavity. The shape of the folds will be 
more comprehensible from the Fig. 37 than from any description I 
can give. They are not all of the same height, but they form two op- 
posite groups, the folds in the center of each group being the highest. 
On either side and between the two groups there are smaller folds. 
Whatever the height of the folds, however, they all have the same gen- 
eral histological character, which is indicated by Fig. 38. The cells 
are large and cylindrical, slightly granular, those near the top of each 
fold being slightly pigmented with brownish matter that obscures their 
definition. The nuclei are large, oval, coarsely granular, and lie in the 
middle or lower parts of the cells. The cells are protected by a delicate 
but very distinct cuticula, in which I can detect no pore-canals, though 
it otherwise resembles the cuticula in the ventriculus. In the center of 
each fold there runs up a thin partition of fibrous tissue (Fig. 38, conn), 
which separates the epithelium of the two sides, and is itself an off- 
shoot of the connective tissue, tunica propria, that intervenes between 
the muscles, mnc, and the epithelial layer. The tracheae ramify through- 
out all the layers outside the epithelium ; one of the main trunks run- 
ning to the wall is shown at Tr. (Fig. 37). It sometimes looked as if 
there were glandular follicles in the bottom of the spaces between the 
folds, but of this I could not make sure. 
Towards the tips of the diverticula the folds decrease in height as the 
diameter of sacks diminishes, until finally they disappear almost com- 
pletely. 
Oastro-ileal folds. — I have now to speak of some very curious and 
striking formations which seem to have escaped notice until now, for I 
find no description of them in any of the works on insect anatomy which 
305 L. «., p. 157. 
306 V. Graber: Zur niiberen Kcnntniss des Proventriculus nnd der Appendices ventriculares bei den 
GriUen nnd Laubbeuschrecten. Sitzber. Wien. Akad. (1869), lix, p. 33. 
3W F. Plateau: Recbercbes sur les Phenomenes de la Digestion cbez les Insectes. Memoires Acad. 
Roy. Belg. (1875), tome xli, p. 75, 
