220 



CCELENTERATA 



dividuals in groups which frequently separate before becoming mature, were once 

 regarded as distinct animals. Praya, Diphyes* (fig. 182), in warmer seas. 

 Sub Order III. CYSTONECT^E. Float greatly enlarged; the ccenosarcal 

 tube reduced, the individuals (no covering scales nor swimming bells) attached 

 to under side of the float. Physalia,* Portuguese man-of-war, stings severely. 

 Sub Order IV. DISCONANTILE. Float a flattened disc; manubrium pro- 

 jects from centre of lower surface. Par pita,* disc. Velella* (fig. 182). 



Class II. Scyphozoa (Scyphomedusae) . 



The Scyphozoa parallel the Hydrozoa in frequently having an alter- 

 nation of generations; the asexual generation being the scyphopolyp or 

 scyphostoma, the sexual an acraspedote medusa. In contrast to the 

 Hydrozoa the asexual stage plays a subordinate role; it is closely similar 

 in all species, and can even be lost (Pelagia), while the medusae are always 

 well developed and present great variety of form. 



The scyphostoma (figs. 183, 184) recalls Hydra, but has a small 

 perisarcal cup around the aboral end. Internally there are four longi- 

 tudinal folds projecting into the gastral cavity and extending from the 



FIG. 18: 



FIG. 184. 



FIG. 183. Scyphostoma of Aurelia aurita (from Korschelt-Heider). k, perisarc 

 cup; pb, proboscis; s, stalk; t, gastral folds; tr, ectodermal funnels. 



FIG. 184. Section of Scyphostoma (from Hatschek). gr, gastric pouches; s, 

 gastric septa; sm, muscles. 



margin of the mouth to the opposite pole. These septa or taniola 

 (fig. 184, s) appear in cross-section as small folds of entoderm supported 

 by a process of the supporting layer containing a muscle band extending 

 down from the peristome (fig. 184). They are important morpholog- 

 ically, since in budding they produce the gastral tentacles (phaccllcz) of 

 the medusa?. Further, they are the- first appearance of the septal system, 

 so strongly developed in the Anthozoa. 



The medusas are large (four inches to four feet or more in diameter) 

 with a slightly arched umbrella, often of almost cartilaginous consistency. 



