306 ELEMENTS OF COMPARATIVE ZOOLOGY. 



ments and inturued oesophagus, and are further distin- 

 guished by the fact that the aperture of the umbrella is 

 partially closed by a thin membrane (velum) lacking in the 

 other jellyfishes. These jellyfishes produce the eggs from 

 which are developed other colonies like that studied. 



FIG. 139. A Hydroid (BougainviUea. After Allman, from Lang. 7i, feed- 

 ing polyp ; rn/c, medusa-buds ; m, a f ree-swiming medusa. At the base 

 are seen the root-like stolons connecting the colony together. 



Here is a point which needs emphasis. From the egg is 

 developed a hydranth which by budding develops numer- 

 ous other hydranths, and each of these in turn, by budding 

 produces several medusae. In other words, we have here 

 au animal which reproduces asexually. These medusae are 



