46 COMPARATIVE ANATOMY AND PHYSIOLOGY. 



that the mesoblast becomes separated into two layers, 

 one of which applies itself to the epiblast, and 

 the other to the hypoblast ; in this way we get 

 the somatopleure and splanclmopleure of 



Fig. 16. Venus' Girdle (Cestus veneria). 



embryologists. All the Metazoa that possess this 

 body cavity may be spoken of collectively as the 

 Cflplomata. In some cases the ccelom remains 

 throughout life in a vory rudimentary condition, and in 

 a few it cannot be said to be developed at all, while in 

 others it would seem to have been lost by degeneration. 

 According to its mode of origin, as an out-growth 

 from the enteron, or by cleavage of the mesoblast, it 

 is spoken of as an eiiteroccele, or a schizoccele. 



