128 
ANATOMY AND PHYSIOLOGY 
sists, as among vertebral animals, of three tunics or 
coats, the mucous , cellular , and muscular , the first 
being internal, and the others superimposed in the 
order in which they have just been named. The 
first is delicate and soft, without any decided texture, 
frequently transparent, and of sucli tenuity that its 
presence is not always easily detected. The second 
layer, (which Strauss names membrane propre , or 
proper shin,) is likewise for the most part smooth 
and thin, although it sometimes becomes thicker and 
spongy. It is generally almost without fibres, but, 
when highly magnified, a few globules or granulations 
appear, arranged transversely in its tissue. These 
have been called by Strauss, gastric glands. Accord- 
ing to Leon Dufour, the membrane in question is 
entirely wanting in hemipterous insects. The mus- 
cular membrane is firm, fibrous, and contractile, sur- 
rounding and protecting the exterior, and distinct 
longitudinal and transverse vessels pervade its tex- 
ture. It is it which causes the peristaltic movement 
of the digestive tube, and it forms the contractions 
and sphincters observable in different parts of it. 
These contractions, as already intimated, form 
various divisions in the intestinal tube which have 
names assigned to them in accordance with their 
functions. The following divisions are recognised, 
the pharynx , the esophagus , the crop, the gizzard \ 
the chylijic ventricle , the slender intestine , the ccecum } 
and the rectum . 
Besides these integral parts of the canal, there are 
various vessels appended to it, which discharge juices 
