]Vi;W VIEWS OF ANIMAL TRANSFORMATIONS. 629 



of the individuals which compose it ? We have no need of hypothe- 

 sis, however, to demonstrate that these colonial organs are the equiva- 

 lents of true individuals. The buds that give birth to the different 

 sorts of individuals in a colony of Hydractinia all grow alike, and re- 



FlG. 2.— NAKED-BTED MEDUSiE. 



main alike for a long time. This is the first presumption in favor of 

 their equivalence. But in the allied type, Podocoryne, we see the hum- 

 ble sac, which represents the sexual individual, replaced by a being 

 more active, more elegant, much more elevated than the Hydra itself, 

 by a transparent medusa, which is detached when it reaches maturity 

 and swims actively in the water, the colony suffering no inconvenience 

 from the change (Fig. 2). These medusse constitute the most general 



Fig. 3.— a, fragment of Cordylophora lacustris slightly enlarged : 6, Bame, showing gonangium ; 

 portion of Syncoryne sarsii, with medusifonn ZoOids budding between the tentacles. 



form of the sexual individuals in the group of Hydroid Polyps, but 

 they are very polymorphic. Their form is modified from one species 



