OF DIGESTION. 



75 



the stomach (5), then the intestine, which is small at first, 



but often enlarged to- 

 wards its termination. 

 This arrangement may 

 be seen by the following 

 diagrams from a beetle, 

 and a land-mollusk, where 

 the same letters indicate 

 corresponding parts (Figs. 

 51, 52). 



207. From the mouth, 

 the food passes into the 

 stomach through a narrow 

 tube in the neck, called 

 the cesophagus or gullet 

 (o). This is not always a 



Fisr. 51. 



Fig. 52. 



direct passage of uniform size ; but there is sometimes a 

 pouch, the crop (c), into which the food is first introduced, 

 and which sometimes acquires considerable dimensions, espe- 

 cially in birds, and in some insects andmollusks (Fig. 51). In 

 the stomach, the true digestive process is begun. The food no 

 sooner arrives there than changes commence, under the influ- 

 ence of a peculiar fluid called the gastric juice, which is se- 

 creted by the glands lining the interior of the stomach. The 

 digestive action is sometimes aided by the movements of 

 the stomach itself, which, by its strong contractions, tritu- 

 rates the food. This is especially the case in the gizzard 

 of some birds, which, in the hens and ducks, for instance, is 

 a powerful muscular organ. In some of the Crustacea and 

 Mollusks, as the Lobster and Aplysia, there are even solid 

 organs for breaking down the food within the stomach itself. 

 208. The result of this process is the reduction of the 

 food to a pulpy fluid called chyme, which varies in its 

 nature with the food. Hence the function of the stomach 

 has been named chymification. The chyme thus formed 



