BEING A WORM 



189 



Septum 

 Vnuscle,--- 



hear-ts 



also 3,4-.S 



seroinal — 

 receptacle 



with fluid which passes from one segment to another through single 

 perforations in each of the septa. The fluid contains ameboid cells, 

 that probably serve as scavengers, and it acts as blood, bathing and 

 nourishing the tissues and carrying away wastes. 



The Digestive Tract and Its Functions 



The food of earthworms, bits of animal or vegetable matter mixed 

 with soil, is taken into the mouth by means of suction. A muscular 

 pharynx, previously moistened by the fluid poured out from small 

 glands in its wall, is able to 

 pull the material into the 

 esophagus, a thin-walled part 

 of the tube which extends from 

 the 6th to the 15th segment, 

 beside whose walls, between 

 segments 10 to 12, there are 

 embedded three pairs of whit- 

 ish structures, the calciferous 

 glands. These glands produce 

 a limy secretion supposed to 

 neutralize the food materials. 

 The esophagus leads into a 

 thin-walled crop, occupying 

 the 15th and 16th segments, 

 which opens into a thick- 

 walled, muscular gizzard ex- 

 tending over segments 17 and 

 18. The latter organ has an 

 internal chitinous wall, and is 

 probably used to macerate bits 

 of undigested food by means 

 of muscular contraction. The 

 remainder of the food tube, ex- 

 tending from the 19th segment 

 to the anus, is called the intestine. Its inner surface is increased by a 

 fold on the dorsal side (typhlosoJc) , while surrounding it there is a layer 

 of yellow-brown tissue cMorogogen cells, which are thought to aid in 

 excretion and possibly digestion of food. The wall of the intestine 

 contains gland cells that secrete at least three kinds of enzymes, which 

 digest starches, fats, and proteins. The digested food is absorbed 



Seminal 

 vesicle.—. 



cConsal 

 vessel 



.pViarxnx 

 .<?5c>p'hag"tc5 



.Caldfe.r<3US 

 glancfs 



.crop 

 intestine 



t/pbloSole 

 rzerve CorcC 



ventral 

 vessel 



three ofhen-.-r^-l 

 vessels *■ 



The earthworm {Lnmhricns ierrestris) 

 opened from dorsal side to show internal 

 structure. (After Sedgwick and \\ ilson.) 



