DIGESTION 



203 



a number of substances, derived from dilTercnt sources, which 

 have the power of changing starch into sugar, but produce this 

 result under different conditions. This indicates a difference 

 in constitution of the ferments. The same is true of the pro- 

 teolytic ferments, for example, pepsin and trypsin are both 

 proteolytic, but the one in acid media, the other in alkaUne, 

 and in Cephalopods there is a ferment which resembles both of 

 these. Generally, in higher animals, there are more kinds of 

 ferments, but each is more circumscribed in its action. Con- 

 versely, in the lower forms, the ferments are fewer in kind but 

 more general in action. So there is apparently in the higher 

 animals a differentiation of ferments to correspond with the 

 structural differentiation of the digestive tract. 



464. In the food vacuole of amoeba the medium first 

 becomes acid but later, at the time when the food particles are 

 disintegrating, the reaction is alkaline. Proteolytic and amy- 

 lolytic ferments are present, and these seem to vary w^ith differ- 

 ent types of Protozoa and the exact nature of those found in 

 amoeba is not certainly know^n. 



465. The fluid of the gastro-vascular cavity of Coelentcrates 

 has no amylolytic powers. There is a slight proteolytic action 

 which probably serves to dissociate large objects so that the 

 particles may be ingested by the entodermal cells. 



466. The digestive fluids of the earthworm and nereis are 

 both tryptic and diastatic. The earthworm covers leaves it 

 means to swallow with saliva and allows them to digest for 

 some time before swallowing them. 



467. The digestive gland of the crayflsh has strong proteo- 

 lytic and amylolytic action in both acid and alkaHne media. 

 Hence, it resembles both gastric and pancreatic digestion of 



D.C., descending colon; Duo, duodenum; Ep.GL, ei)iglollis; G'./:}., g;ill bhulder; 

 II. D., hepatic duct; //, ileum; OC, oral cavity; Ocs, ocsojihaKus; 1\ pyloric portion 

 of the stomach; Pa, pancreas; P. D., pancreatic duct; 7V/, pharynx; P.G., parotid 

 gland; R, rectum; S, stomach; S.L., sublingual gland; S.M., sul)maxillary gland; 

 T, tongue; T.C., transverse colon; Tr, trachea; v. A., vermiform appendix. 



