12 GENERAL SURVEY OF THE ANIMAL KINGDOM. 



belongs only to the adults) ; that in most types a body-cavity or ccelom 

 is developed ; that the embryo consists of three germinal layers (external 

 ectoderm or epiblast, internal endoderm or hypoblast lining the gut, 

 and a median mesoderm or mesoblast lining the body-cavity). In the 

 next two classes (Ccelentera and Sponges) the conditions are different, as 

 may be expressed in the following table, though it is open to question 

 whether the contrast is quite so great as it seems : — 



Ccelentera. — This series includes jelly-fishes, sea-anemones, 

 corals, zoophytes, and the like, most of which are equipped 



Fig. 16.— Sea-anemones on back of hermit-crab. 

 — After Andres. 



with stinging cells, by means of which they paralyse their 

 prey. All but four or five are marine. The body may 



