HYDROZOA. 



45 



the polyps are ovoid and provided with scjittered eiiform . ..^ a, 

 tentacles. 



The dried specimens of Ceratella and Cliitina in Case 3a arc- 

 composed of a dense network of horny tubes. In life the surface of 

 the branches is covend with large club-shaped polyps provided with 

 scattered knobbed tentacles. 



Thecaphoha (or Oali//itob/us(ea-Lepto)imhi.s(r}. This group in- 

 cludes many of the more familiar forms of zoophytes (Case 3 a, u). 



Fill. •;. 



A. Clavatdla proUfera (magnified) ; at base, clusters of generative polyps, one of 

 which is nearly ready to become detached, n. Free creeping generative jwilyp 

 or Medusa, highly magnified ; 6, tiie siime slightly eiihirged. (Afti-r Hincks.) 



The feeding polyps can be retracted into horny cups, and the 

 generative polyps (which are budded off from a blastostyle, and 

 which may be fixed or free-swimming) are enclosed in a horny 

 capsule. The MedustB (Leptomednsa') develop the eggs in the 

 radial canals. There are three sub-groups — the Campanuhiriua, 

 with stalked cups, the Sertularina, witli sessile cups, and thi' IMuinu- 

 larina, in which occur little supplementary cups i-alled nematophore-s 

 containing an offshoot from the common body substance of the 

 coloiiv loaded with thread-cells. 



