Morphology of Organs. 



i6i 



is perfectly independent of the coelom, and generally this 

 independence is shown by the different character of the 

 enclosed fluids. Thus, in the earthworm the blood is red, 

 with a few corpuscles; in the case of the coelomic fluid we 

 have numerous and large corpuscles floating in a colourless 

 fluid. In order to emphasize its distinctness the term 

 "hffimoccel" is often applied to the vascular system in its 

 entirety. But though the hsmocoel is distinct from the 



CCEL 



H«.M 



H/5.M. N 



Fig. 74. — Transverse section of an embryo Earthworm, to illustrate independence 

 of coelom and heemocoel. (After "Wilson.) 



Ent, gut ; CcEL, coelom ; H.EM, haeraoco?l ; n, nerve-cord. 



coelom in its development, there is sometimes a connection 

 between the two. Thus, in the vertebrates the lymphatic 

 system opens, on the one hand, into the coelom, and, on the 

 other, into the hsemocoel. In simpler animals the channels of 

 the vascular system have not always proper walls. In the 

 majority, however, they have, and then tend to become tubes 

 of regular calibre. A larger or smaller part of these tubes may 



