96 Descriptive Zoology. 



as we have just noted. There is also in each segment 

 (except a few at the two ends of the body) a pair of simple 

 kidneys. Each kidney is a tube opening freely into the 

 body cavity at its inner end, while the other end opens to 

 the outside through a small aperture in the body wall below 

 (or sometimes above) the upper row of bristles. This long 

 tubular kidney is thrown into loops, and there is consider- 

 able variation in its diameter at different points. Each 

 tube begins as an open funnel which is lined with cilia. 

 The oddest fact about these tubes is that each kidney begins 

 in one segment and ends in another; the funnel is in the 

 back part of the segment and the tube from it soon passes 

 through the partition behind it, the bulk of the tube lying 

 in the segment posterior to the one in which it began. 

 These tubes absorb waste matter from the liquid of the 

 body cavity, and convey it to the outside. 



The Nervous System of the Earthworm. This is a chain 

 of nerve centers or ganglions along the ventral part of the 

 body cavity, lying under the intestine. In each segment is 

 a ganglion, and these are connected by a nerve cord run- 

 ning lengthwise. Though apparently single, the nerve cord 

 and chain are really double, the two ganglions and cords 

 being so closely applied and fused that they appear as one. 

 The shortness of the segments brings the successive gan- 

 glions so near together that they are not very distinct. In 

 the anterior region the double nature of the cord is appar- 

 ent. Under the anterior part of the pharynx the two strands 

 of the cord separate, one passing up on each side of the 

 pharynx to a large ganglion, the two ganglions lying closely 

 side by side, forming the " brain." Thus a ring is formed 

 around the pharynx, which is called the " nerve ring " or 

 " esophageal collar." From all the ganglions nerves pro- 

 ceed to the surrounding organs. 



