STRUCTURE OF THE STOMACH. 
213 
«aual is our present knowledge so unsatisfactory as of this. The few 
observations that have been made are eminently incomplete. It is 
known that there is no thick cuticula ; that the muscular layers are less 
powerful than in other parts, and certain other details, which a brief ex- 
amination suffices to clear up. Frey and Leuckart 297 pointed out that the 
walls of the stomach were not folded, but that the secretory surface was 
increased in some cases (in many Coleoptera, for instance) by the epithe- 
lium and connective tissue forming villi, a fact already noticed by H. 
Meckel. 298 Sirodot 299 subsequently showed that there are also gastric 
glands in many insects, and describes particularly (1. c, pi. 13, Fig. 3) 
how in the field cricket the gastric follicles occupy the interspaces of a 
network formed by the sinuous fibers of the connective tissue, " tunica 
propria " auct. I have found essentially the same structure to exist in 
grasshoppers (Caloptenus and Oedipoda). The description of the 
minute anatomy of the veutriculus which Leydig gives 300 is very meager 
and insufficient, while that given of the epithelium and glands in the 
stomach of the cockroach by von Basch 301 will probably require some 
modification. 
The walls of the stomach are composed of an internal epithelium, a 
layer of connective tissue, an inner layer of unstriated circular muscu- 
lar fibres, and an external layer of longitudinal fibres of striated muscle. 
In studying these layers I have found it best to begin by viewing them 
from the inner surface. If the walls of the stomach be spread out and 
stained and then mounted in glycerine or Canada balsam, it will be seen 
that the nuclei of the epithelium are not uniformly distributed, but there 
are little clusters, each of which corresponds to a small gland or follicle ; 
it can be further seen that each gland has a cavity or duct ; each follicle 
lies in a cup of connective tissue, which separates it from its neighbors. 
If a piece of the wall spread out on a glass slide in a drop or two of 
water, is gently brushed with a fine camel's hair pencil, the epithelium 
•can be removed, and if the specimen be then stained and mounted the 
structure of the remaining layers will be displayed as shown in Fig. 39. 
The connective tissue, tunica propria, forms a somewhat irregular net- 
work, 302 the meshes-of which vary in size only between certain limits. In 
the figure the network is drawn somewhat darker than it appears in 
reality, in order to make it stand out more plainly. The spaces of the 
network are the cups before mentioned in which the gastric fol- 
licles lie. The tissue has a fibrous character and also forms the bottoms 
of the cups, as is shown by sections. Underneath the connective tissue 
follows the internal muscular coat, In. m., composed of a great number 
297 Frey und Leuckart: Anat. Physiol. TJbersicht. Thierreichs, 1855, p. 114. 
^ileckel. Mikrographie einiger Driisenapparate niederer Seethiere. Miiller's Arch., 1846. Die Ein. 
theilung ties Darmcanals bei den Insekten. Par. 4, p. 23. 
Sirodot Recherches sur les secretions chez les Insectes. Ann. Sci. Nat. Zool. Ser. 4. Tome X, p. 
183 (1858). 
300 Leydig. Lohrbuch der Histologic, 1858, p. 337. 
* 01 Basch, 1. c, Wien. Akad. Sitzber., xxxiii, 248,ff 
302 Compare Sirodot, 1. c, PI. 13, Fig. 3. 
