CHAPTER 6 



CIRCULATION AND RESPIRATION 



In most annelids there is a well developed blood vascular system 

 consisting of longitudinal dorsal and ventral vessels, a plexus on 

 the wall of the gut and regular lateral segmental vessels supplying 

 the body wall, nephridia, etc. Leeches do not conform to this 

 pattern. The nearest approach is found in the rhynchobdellid 



Pulsatile vesicle 



Acanthobdella 



Glossiphonia 



Piscicola 



Hirudo Erpobdella 



Fig. 27. Comparative diagrams illustrating the progressive 

 loss of median dorsal and ventral blood vessels and their func- 

 tional replacement by lateral coelomic sinuses with muscular 

 walls in various leeches. Coelomic sinuses open circles; dorsal 

 and ventral vessels solid circles; thick-walled circles indicate 

 coelomic sinuses with muscular walls. 



leeches which have small longitudinal vessels but no segmental 

 ones. These longitudinal vessels lie in coelomic sinuses (Fig. 27) 

 and it is the coelomic fluid which circulates to all parts of the body, 

 carrying out gaseous exchange and transporting food materials 



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