CCELENTERATA. 



167 



class of the Coelenterata. They are medusoid (jelly- 

 fish-like) animals, and receive their name (comb-bearers) 

 from possessing parallel bands of cilia. They have a 

 special modification of the thread-cell, which is sticky 

 at the end, and fixes instead of stinging its prey. They 

 have sense-organs similar to those of the medus^. 

 Some are nearly round, but though they have a symi- 

 metry in some respects radial, they have traces of 

 acquired bilateral structure due to an active swimming 

 life ; and some are bilaterally flattened. They propel 

 themselves by means of active cilia. The gastric 

 cavity, which is called the infundihulum, is affected 

 by this bilateral symmetry, so that it assumes a 

 compressed form. The Gi/dippo is a common kind in 

 English seas: it is about the size of a marble, and is 

 a very pretty form, with two long ciliated tentacles. 

 The highly phosphorescent " Venus' Girdle " also be- 

 longs to this group (Fig. 39). 



Fig. 40.— The Organ Coral, Tiibipora musica, one of the Aloyonaria (p. 165). 



