HYDROZOA. 



45 



filiform Case 3. 



the polyps are ovoid and provided with scattered 

 tentacles. 



The dried specimens of GerateUa and Chitina in Case 3a are 

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

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

 scattered knobbed tentacles. 



Thecaphora (or Cali/ptoblastea-Leptomeduscn). This group in- 

 cludes many of the more familiar forms of zoophytes (Case 3 A, b). 



Fig. 6. 



A. Clavatella prolifera (magnified) ; at base, clusters of generative polyps, one ot 

 which is nearly ready to become detached. B. Free creeping generative polyp 

 or Medusa, highly magnified ; b, the same slightly enlarged. (After 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 Medusa3 (Leptomedusaj) develop the eggs in the 

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

 with stalked cups, the Sertularina, with sessile cups, and the Plumu- 

 larina, in which occur little supplementary cups called nematophores, 

 containing an offshoot from the common body substance of the 

 colony loaded with thread-cells. 



