340 



THE EARTHWORM 



CHAP. 



The excretory organs of 



the earthworm consist of 

 little tubes called neph- 

 ridia, of which each meta- 

 mere except the first 

 three and the last 

 possesses a pair, one on 

 either side (Figs. 81-84). 

 You will remember that 

 in the frog all the urinary 

 tubules are connected 

 together to form a pair 

 of kidneys, each with a 

 single duct communicat- 

 ing with the cloaca. In 

 the earthworm each neph- 

 ridium is a long and 

 extremely delicate tube, 

 arranged in three main 

 loops (Fig. 84), opening 

 at one end into the ccelome 

 by a nephrostome and at 

 the other communicating 

 with the exterior directly 

 (Fig. Si). 1 The tubes are 

 attached to the posterior 

 faces of the septa. Each 

 nephrostome (a) is cili- 

 ated, and projects 

 through the correspond- 

 ing septum so as 

 to communicate with 

 the segment of the 

 body-cavity next in front of that in which the main part 



1 In the frog the nephrostomes lose their connection with the 

 nephridia, and open in the adult into the renal veins (Fig. 47, 

 p. 146). 



FIG. 84. A nephridium of Lumbricus, 

 showing the three main loops into which 

 the different parts of the tubule are ar- 

 ranged, as well as the different portions 

 of the tubule, (x about 30.) 

 a. nephrostome ; b, b, b, slender portion of 

 the tubule into which the nephrostome 

 opens ; c , c, second ciliated portion ; d, 

 glandular portion ; e, muscular portion ; 

 e end of e at which the nephridiopore 

 opens. (From Gegenbaur.) 



