BRITISH ZOOPHYTES. 133 



straight^ and on the pinna3 on the other side they 

 curve considerably over the calycles. 



The gonothecaa are not developed into corbulae, but 

 are somewhat pyriform in shape. 



Sub-Oeder III. GYMNOCHROA. 



(Eleutheroblastea, Allman.) 



FAMILY L HYDRIDE. 

 Genus Htdka, LinncBus. 



Polypites locomotive, single, destitute of polypary, 

 cylindrical or subcylindrical, with a single series of 

 filiform tentacles round the mouth and a discoid adhe- 

 sive base, (j-onozooids always fixed, developed in the 

 body walls.— T. H. 



The structure of the members of this genus has been 

 already fully described in the descriptive chapter. 

 The dijQferent species are all inhabitants of fresh water. 



The ease with which specimens of Hydrge can be 

 secured makes them objects of constant interest and 

 experiment. The most popular experiments are those 

 conducted with a view to test their vitality. From the 

 times of Baker and Trembley to the present, observerB 

 have been at work trying to what extent this much- 

 suSering animal would bear mutilation. 



Baker, in the tenth chapter of his work on " The 

 Polyp/' gives a course of experiments, amongst which 

 are the following, which show an advancing scale of 

 destructiveness and torture contrived with singular 



