CCELENTERATA. 149 



While we call this a larva, it must be remembered 

 that it is equivalent to a stage which is still enclosed 

 in the egg, in higher and more slowly growing animals. 

 The beginner must guard against the mistake of sup- 

 posing that all larvse are equivalent : the larva of a 

 higher form, on the contrary, usually represents the 



Fig. 30. — Specimens of the Brown or Long-armed Hydra, Hydi-a /usca, ad - 

 herin^ to a bit of wood : a, several individuals, natural size ; 6, an individual 

 with two asexaally produced buds, enlarged. 



adult stage of a lower form, from some variety of 

 which, accoi-ding to the principles explained on p. 55, 

 it is then supposed to be descended. 



One of the simplest forms of the Ccslenterate animal 

 is found in Hydra, the fresh-water polyp (p. 131). 



Colonial or Compound Animals. The most 

 remarkable feature of this group is the tendency to de- 



