144 



ORGANS AND ORGAN SYSTEMS 



of this activity are liberated into the coelom by the frag- 

 mentation of the cells and then carried to the outside by 

 the nephridium. 



Dorsal Pores. Excretion is also carried on to a limited extent 

 through dorsal pores situated in the annuli in the mid-dorsal 

 line. 



am 



m 



s 



FIG. 59. Transverse section of the earthworm behind the clitellum. a.c., 

 Cavity of the digestive tract; c, cuticle; coe, coelom; c.m., circular muscles; c.v., 

 circular vessel; d.v., dorsal vessel; hy, hypodermis; l.m., longitudinal muscles; 

 n.c., ventral nerve chain; p.e., peritoneal endothelium; s, seta; s.g., setigerous 

 gland; s.i.v., subintestinal vessel; s.m., muscle connecting two groups of setae on 

 the ^ame side; /y, typhlosole. (From Sedgwick and Wilson.) 



G. THE MUSCULAR SYSTEM. The main muscular system of the 

 earthworm is relatively simple, consisting of two walls of muscle 

 fibers forming a continuous sheath from anterior to posterior 

 ends of the worm. Being united with the skin to form the 

 body wall it is known as dermal musculature. The inner 

 wall consists of longitudinal fibers running from somite to 

 somite, and their contraction results in drawing head and 



