CH. I] EARTHWORMS AND LEECHES 11 



Each segment of the body, with the exception of the first 

 three and last one, possesses a pair of these organs. The 

 funnel-shaped mouth lies in the segment anterior to that 

 which contains the rest of the tube, the first part of the 

 duct perforating the intervening septum. Each tube is 

 divisible into several regions; the portion next to the 

 funnel is ciliated, the next part glandular, and the third 

 section, which functions as an expellent bladder, muscular. 

 The tubes are abundantly supplied with blood, from which 

 they eliminate waste substances in the form of uric acid. 

 In this work they are assisted by the "yellow" or chlora- 

 gogen cells which form so conspicuous an external covering 

 to the intestine, especially along the line of the typhlo- 

 sole, the groove of which structure is closely filled with 

 them. The apparent connexion of the chloragogen cells 

 with the alimentary system is accidental. They are in 

 reality closely applied to the outer walls of the dorsal 

 blood vessel and its intestinal offsets. They originate 

 from the amoeboid corpuscles of the ccelomic fluid which 

 occupies the body-cavity (ccelom). Certain of these 

 attach themselves to the walls of the blood vessels and 

 extract from the blood yellowish-brown substances and 

 thereby become converted into chloragogen cells. When 

 filled with these coloured bodies they detach themselves 

 from the walls of the blood vessels* and float about in the 

 ccelornic fluid. Their contents then break down into the 

 blackish debris which is often found in the nephridial 

 tubes and is by them conducted to the outside (Kiiken- 

 thal 1 , and Claparede 2 ). Foreign substances such as indigo, 



1 Jena. Zeit. vol. xvm. 1885. 2 Zeit. wiss. Zool. xix. 1879. 



