222 



COLLEGE ZOOLOGY 



tions of the dorsal trunk, beginning at the posterior end and 

 traveling quickly anteriorly. These contractions are said to be 



S7l 



CV 



FIG. 155. Diagrams showing the arrangement of the blood-vessels in the 

 earthworm. A, longitudinal view of the vessels in somites VIII, IX, and X. 

 B, transverse section of same region. C, longitudinal view of the vessels in 

 the intestinal region. D, transverse section through the intestinal region. 

 af.i, afferent intestinal vessel; cv, parietal vessel; ef.i, efferent intestinal 

 vessel; ht, heart; it, intestine; il, intestino-tegumentary; nl, lateral-neural 

 vessel ; oe, oesophagus ; s, septa ; sb., ventral vessel ; sn., sub-neural vessel ; 

 sp., dorsal vessel ; ty., typhlosolar vessel. (From Bourne, after Benham.) 



peristaltic, and have been likened to the action of the fingers in 

 the operation of milking. Valves in the walls of the dorsal trunk 

 prevent the return of blood from the anterior end. In somites 



