OF DIGESTION. 363 



middle one., or proventriculus, is wanting. Thus the chylifying por- 

 tion of the intestine is formed in the several orders according to the 

 differences of their food; for greater detail I refer to 105. 



If we now investigate the digestion of solid substances by the assist- 

 ance of the proventriculus we shall find that those, when of the animal 

 kingdom, are swallowed wholly unchanged but in pieces, but, when 

 of the vegetable kingdom, they are already much comminuted and 

 intimately mixed with the saliva. They consequently first arrive at 

 the large crop placed in front of the proventriculus, which in some 

 cases, as in the Dylici, is thickly beset internally with glands, and the 

 superior surface of the internal tunic is occupied with wrinkles, horny 

 lines, and teeth (PI. XVII. f, 5 7-)- The secretion of these glands, 

 is a dark brown sharp corrosive fluid, which strongly smells like Russia 

 leather, it supplies the place of saliva, envelopes the food, makes it soft, and 

 thus prepares it for digestion. The food, after having thus remained 

 a short time in the crop, advances by degrees into the infundibuliform 

 orifice of the proventriculus, and thence into its narrow cylindrical or 

 star-shaped cavity, where it is easily comminuted, and transformed into a 

 uniform pap-like consistency. To produce this we observe in the crop, and 

 particularly in the proventriculns, a peculiar motion, which consists of 

 an alternating expansion and contraction. This contraction commences 

 at its anterior extremity, and gradually advances to the end of the 

 proventriculus, whilst the earlier contracted portion again expands. It 

 thus greatly resembles the progressive advance of worms and footless 

 larvse ; it is called the peristaltic motion. It is most distinctly observed 

 in the proventriculus, which also, of all the parts of the intestine, is sup- 

 plied with the largest fasciculi of muscles ( 104), and it here appears 

 as a contraction and distension of its internal cavity, produced by its 

 rhythmical contraction and expansion. By means of this contraction 

 the teeth and horny plates rub against each other, and thus grind the 

 food into a simple uniform pap, which is called chyme. In this state 

 we then find it in that portion of the intestine lying behind the 

 proventriculus, which, as we have above seen, is supplied throughout 

 or partially with short blind appendages. These appendages, according 

 to Rengger *, become shortened when the intestine is filled with food, 

 and they then appear merely as lumps upon its surface. Its contents is 



* Physiologische Untei'suchungcn uber den Thieriachen Haushiilt tier Insckteu. 

 Tubing. 11)17. Hvo. 



