COMI'AKISON WITH SPONGES. 27 



Larva is a "planule," a polypite, 

 an Amoeba, or a Medusa. Hincks 

 states that in nearly all species the ova 

 develop into planules, and thence become 

 modified into polypites ; but in the fresh water 

 Hydra and a few other species, the ova at 

 once take the form of polypites. One instance 

 he cites in which the egg gives place to an 

 amoeboid form. There are some cases also, 

 where the ovum of the hydroid-medusa does 

 not revert to the fixed hydroid state but is 

 hatched out a Medusa. 



Hydroids compared with the 

 sponges. Having briefly considered the 

 nature of the Hydroids, a few remarks 

 may not be out of place to state in what 

 respect they differ from their neighbours on 

 either side. 



The group of organisms immediately 

 below the Hydroids, is the Sponges. They 

 are a peculiar and somewhat anomalous group 

 of animals. It is difficult to define their 

 actual affinities.. 



Suppose, however, we take a densely - 

 branching hydroid, such as Eudendrium 

 raineum^ Pallas and deprive the animal colony 



