HYDROZOA. 
45 
the polyps are ovoid and provided with scattered filiform Case 
tentacles. 
The dried specimens of Cercitella and Ghitina 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 Galypto & lasted- Leptomedusce . ) . This group in- 
cludes many of the more familiar forms of zoophytes (Case 3 a, b). 
Fig. 6. 
a. Clcivatella prolifer a (magnified) ; at base, clusters of generative polyps, one of 
which is nearly ready to become detached, b. Free creeping generative polyp 
or Medusa, highly magnified ; &, 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 Medusae (Leptomedusae) 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. 
