40 HYDROZOA. 



Among the varied appendages attached to the 

 coeno.'^arc of the PhysojjJwvkke occur certain pro- 

 cesses of doubtful nature, which Kolliker and some 

 other observers appear disposed to regard as organs 

 of touch (fig. 22). The * hydrocysts,' or feelers, 

 for so have these bodies been termed, bear some 

 resemblance to polypites in their structure and 

 mode of attachment, but differ from them in pos- 

 sessing caecal extremities, beneath which large 

 thread-cells are embedded. In some genera they 

 are with difficulty distinguished from polypites in 

 a young state of development. 



8. Reproductive Organs. — Processes of -the 

 body-wall, within which are developed true gene- 

 rative organs, the ^ spermaria ' and ' ovaria,' con- 

 stitute the reproductive apparatus of the Hydrozoa. 

 These processes are always external, and are re- 

 markable for the interesting series of modifications 

 which they present among the several members of 

 the class {figs. 6 and 7). 



In Hydra, as already shown, they are of the 

 simplest possible structure, differing from other 

 parts of the body-wall in their contents alone. 

 Such, also, is their aspect in Lucernaria, Pelagian 

 and, probably, all the MedusidcB. 



In the Corynidw, Sertularidce, Ccdycophoiddce, 

 and PhysophoridWf the reproductive bodies appear 

 externally as distinct buds, or sacs, for which Pro- 

 fessor Allman has proposed the name of * gono- 

 phores.' 



The simplest kind of gonophore consists of a 

 well-defined protuberance from the body-wall, the 

 * sporosac,' containing within its substance ovaria 



