66 



BRANCH ANNULATA 



truded and -retracted. The radially arranged muscular fibers 

 which run from the pharynx to the 

 body wall retract the pharynx and at 

 the same time dilate it. Back of the 

 pharynx is the narrow esophagus, with 

 a pair of pouches and two pairs of 

 calciferous glands, which communicate 

 with these pouches and which contain 

 a limy fluid. Posterior to the pharynx 

 i the thin-walled crop, and back of 

 this is the very thick-walled rounded 

 gizzard, with its tough, chitinous lin- 

 ing, in which the food is ground by 

 sand, and from which the intestine ex- 

 tends to the anal opening in the pos- 

 terior segment. 



The typhlosole, a prominent ridge 

 extending along the middle of the dor- 

 sal surface of the intestine and dipping 

 down into the interior, renders the 

 hollow of the intestine crescent shaped. 

 This typhlosole increases the absorb- 

 ing surface and is well supplied with 

 blood-vessels. 



The circulation is carrried on in a 

 well-developed system of blood-vessels. 

 The dorsal tube extends along the 

 median line of the dorsal surface and 

 is plainly seen in the live earthworm. 

 The forward movement of the blood can 

 usually be seen . The ventral blood-ves- 

 sel lies below the alimentary tube. In 

 this ventral blood-vessel the blood is pro- 

 pelled backward by the peristaltic action 

 of the tube. The three smaller blood- 

 tubes, the subnural and two lateral 

 nural tubes, lie close to the nerve cord. 



Each segment has a transverse vessel connecting the dorsal 

 and ventral blood-vessels. Those from the sixth to the eleventh 



Fig. 50. Earthworm 

 dissected to show aliment- 

 ary tube, al. t. (From 

 Jordan and Kellogg, 

 " Animal Life," D. Apple- 

 ton and Co., Publishers.) 



