214 



ZOOLOGY 



water animal, and a few kinds of small fresh-water 

 medusoids (Hydrozoa) are known. Great excitement 

 was caused, many years ago, by the discovery of the first 

 of these medusoids in the water-lily tank in the Botanic 

 Garden in Regent's Park, London. 



iiydrozoa The Hydrozoa are remarkable for the branching 



colonies of many of the species. This type of structure 

 may be thought of as due to a budding process, - - the 

 buds, as in a plant, remaining attached, with nourish- 

 ment flowing from one to the other. It results from 

 this that specialization is possible, and we find the indi- 

 viduals or persons of the colony taking on different func- 

 tions. Some feed, others reproduce, while others have 

 stinging properties and serve for defense. On examin- 



^VrfT^ 8 " 



i \ 



I! \ \ 

 I 



Drawing by W. P. Bay (after Nutting) 



FIG. 4g. A, a small portion of a colony of Obelia commissuralis, one of the Hy- 

 drozoa, common on American coasts, hy, hydranth in a hydrotheca; gon, a gon- 

 gangium containing young medusa. B, a medusa; stat, statolith ; greatly enlarged. 



