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TEXTBOOK OF ZOOLOGY 



terior to the hearts the dorsal vessel carries the blood posteriorly 

 and the ventral vessel carries it anteriorly. The circulatory system 

 is equipped with numerous valves which keep the blood from flow- 

 ing in the wrong direction. 



fieart 



Dorsal vessel 



Intostlno-tegxuueniai; 

 -— — vessel 

 ,- Ventral vessel 



Sub-neural vessel 



Septa 

 Dorsal vessel 



Septa jl IX Septa 



Intestlnotegtimentary 

 vessel 



VIII 

 Dorsal vessel 



CEsopbagus 



Typhlosolar 



vessel 



Ventral vessel 



Sub-neural vessel £ 



Efferent Intestinal vessel; 



Kephridium 

 Lateral-neural vessel 



Afferent intestinal vessel 



Ventral 

 vessel 



Sub-neural vessel 



Dorsal vessel 

 Typhlosolar vessel 



Ventral vessel 

 Sub-neural vessel 



Parietal vessel 



Fig. 106. — Circulatory system of the earthworm. A, longitudinal view of vessels 

 In somites VIII, IX, and X ; B, transverse section of same region ; C, longitudinal 

 view of the intestinal region ; D, transverse section of the same region. (From 

 Hegner, College Zoology, published by The Macmillan Company, after Bourne, 

 after Benham.) 



Respiratory System 



Respiration in the earthworm is carried on through the skin 

 which is well supplied with blood. Since the animal always lives 

 in a moist environment, this type of respiration is possible. 



Excretory System 



The function of excretion is cared for principally by the paired 

 nephridia, which are found in each segment except the first two and 

 the last one. A single nephridium consists of a ciliated funnel (the 

 nephrostome) , a thin coiled tube, and a nephridiopore. The cilia of 

 the nephrostome create a current which takes the fluid containing 



