INTESTINE. 



57 



MI) 



Al>\ 



repeated mechanical action (masticatory stomach of Cray-fish) or by 



the secretion of digestive fluids (pepsin) furthers digestion; or it 



may, as in birds, subserve both these functions. From the stomach 



the food passes into the mid-gut. Dilatations and out-growths of the 



buccal cavity give rise to cheek and 



throat pouches, of the ceosphagus to 



the crop, of the stomach to blind sacs 



which serve as reservoirs for the food 



(stomach of Ruminants) (figs. 47 & 48). 

 In the middle 

 section of the 

 alimentary ca- 

 nal,or intestine, 

 the digestive 

 processes, al- 

 ready c o m - 

 menced in the 

 mouth by the 

 action of the 

 salivary secre- 

 tion and con- 

 tinued in the 

 stomach by the 

 action of the 



pepsin of the gastric juice (upon albumins 

 in an acid solution), is completed. The food 

 constituents which have been so far unacted 

 upon (chyme) are in the intestine submitted 

 to the action of the secretions of the liver, 

 pancreas, and intestinal glands, and by them 

 converted into the chyle, \vhich is absorbed 

 by the intestinal walls ; the albumins being 

 converted, as in the stomach, into soluble 



FIG. 49. Alimentary oanai of modifications by the action of trypsin 

 a butterfly. 7? proboecis (ma- / act i n g however, only in alkaline solutions). 



xillSB) &2?, Sfilivsxy 2n.Eincls ; ^ * 



oe, ossophagus; s, sucking The intestine often attains a great length, 

 and becomes divided into regions possessing 

 a different structure ; e.g., in the intestine of 

 mammals three regions can be distinguished duodenum, jejunum, 

 and ileum. Its surface is, as a rule, increased by the develop- 

 ment of folds and villi, and sometimes of outgrowths. Amongst 



FIG. 47. Alimentary canal and ac- 

 cessory glands of a caterpillar. 

 O, mouth ; Oe, oesophagus ; Sp D, 

 salivary glands; Se, spinning 

 glands ; MD, intestine (mid-gut) ; 

 AD, rectum (hind gut) ; MG, Mal- 

 pighian tubes. 



stomach ; Mg, Malpighian 

 tubules; Ad, rectum. 



