128 ANATOMY AND PHYSIOLOGY 



sists, as among vertebral animals, of three tunics o 

 coats, the mucous, cellular, and muscular, the firs 

 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 such tenuity that it 

 presence is not always easily detected. The secom 

 layer, (which Strauss names membrane propre, o 

 proper skin,) is likewise for the most part smoot 

 and thin, although it sometimes becomes thicker an< 

 spongy. It is generally almost without fibres, but 

 when highly magnified, a few globules or granulation 

 appear, arranged transversely in its tissue. Thes 

 have been called by Strauss, gastric glands. Accord 

 ing to Leon Dufour, the membrane in question i 

 entirely wanting in hemipterous insects. The mus 

 cular membrane is firm, fibrous, and contractile, sur 

 rounding and protecting the exterior, and distinc 

 longitudinal and transverse vessels pervade its tex 

 ture. It is it which causes the peristaltic movemen 

 of the digestive tube, and it forms the contraction 

 and sphincters observable in different parts of it. 



These contractions, as already intimated, form 

 various divisions in the intestinal tube which hav 

 names assigned to them in accordance with thei 

 functions. The following divisions are recognised 

 the pharynx, the esophagus, the crop, the gizzard 

 the chylific ventricle, the slender intestine, the ccecum 

 and the rectum. 



Besides these integral parts of the canal, there ar 

 various vessels appended to it, which discharge juice 



