220 Elementary Biology. 



Obelia is one of the salt-water Hydrozoa, variable in size, 

 but seldom reaching a greater height than six inches. It is 



FIG. 113. PORTION OF A COLONY OF Obelia ^enlcnlata. 



a, c, coenosarc ; l>, perisarc ; d, ?ooid ; c, sexual zooid with rudimentary 

 gonophores. 



fixed to the rock by a network of root-like filaments, which, 

 however, are only superficially comparable to roots. The 



