PHYSIOLOGY OF THE INVERTEBRATA. 



257 



(2) The Oligochoeta. — The renal system of Zumhricus consists 

 of a large number of coiled tubes (Fig. 47) distributed in pairs, 

 one pair ia each somite of the body. Each tube or segmental 

 organ (nephridium) consists of three distinct parts — (a) A 

 much-convoluted thin portion, terminating in a funnel-shaped 

 opening ; (h) a thick-walled glandular portion ; (c) a thick 



Cuticle. <■ 

 Epidermis. 



Circular mus- «■ 

 cular layer. 



Longitudinal <■ 

 muscular 

 layer. 



Outer loop of ^ 

 nephridium. 



External 

 opening of 

 nephridium, 



» Dorsal vessel. 



» Middle loop of 

 nephridium. 



Typhosole. 



■* Hepatic cells, 

 so-called 

 " liver." 



Inner loop of 

 nephridium. 



» Epithelium of 

 intestine. 



^ Ventral v. 



^ Coelom. 



^ Internal open- 

 ing of neph. 



^ Vent, nerve 

 cord. 



> Subneural 

 vessel. 



Fig. 47. — Nephridium of Lumbricus. 



muscular portion (the outer loop), which opens externally by 

 an aperture near the ventral side of the body. The nephri- 

 dium as a whole lies on the posterior side of the septum, but 

 the funnel-shaped aperture opens on the anterior surface ; 

 that is to say, into the cavity of the segment in front of that 

 in which the main body of the nephridium lies. This is the 

 case in every segment containing these organs. The septa, 

 or mesenteries dividing the body into segments, are richly 



K 



