PRINCIPLES OF PHYSIOLOGY 85 



PARAMECIUM HYDRA 



Dorsal vessel-] Ho^scrhs 



EARTHWORM 



Blooci 

 vessds 



NEMERTEA 



num 



rHearb 



Ventral Subnearal 

 •-vessel '-vessel 



Ostium^ I rPericardial sinuS 



■<«> -^ ~^ ^ 



^ '^^CRAYFlteH'^^ 



Heart 



p^"" 



CAT 



Figure 5.2. The circulatory systems of paramecium, hydra, nemertea, earthworm, 

 crayfish and cat. 



