PREVIOUS INTERPRETATIONS OF CNIDARIA 189 



and overshadow the polyp generation as a whole so that the 

 latter frequently gives the impression that it were a larval 

 form only. 



It is easy, after everything we have learned about the intesti- 

 nal system of scyphomedusae, to understand correctly this 

 system as it occurs in hydromedusae. Since there are no sarco- 

 septa in Hydrozoa, there is also no division of their intestine 

 into a central part, the stomach, and into the four gastral 

 pockets. Attempts were made earlier to find something similar in 

 the formation of the medusa buds. This has been an important 

 contribution made by Goette (1907) whose suggestion has been 

 supported by Hadzi (1909) and by Kiihn (1914). He dis- 

 proved the older interpretation of the development of the 

 medusae buds in Hydrozoa. The intestinal diverticula of tenta- 

 cles represent the starting point for the formation of the 

 peripheric gastrovascular system of hydromedusae, a situation 

 which is quite different from the one we have found in scypho- 

 medusae. These diverticula have become elongated when the 

 cup -shaped part has been extended, thus when the umbrella 

 has been developed. This has led to the development of the 

 radial canals. Also here, as in Scyphozoa, the basic number of 

 these diverticula has been four. An additional circular canal 

 has been developed due to the tendency of their intestine 

 to form diverticular This has finally, even if not generally, led 

 to a secondary polymerization of these canals which especially 

 took place in larger species either by way of a centrifugal 

 growth of these canals from the stomach, or to a centripetal 

 growth of these canals from the circular canal (in some Tra- 

 chylinae, etc.). 



As a conclusion, we can state that the changes of the digestive 

 system of Cnidaria can be perfectly well understood if viewed 

 from our standpoint: in polyps which have become sessile 

 animals, a simplification ot this system can be observed so that 

 only a smooth intestinal wall has been preserved, while at the 

 same time only the intestinal diverticula ot tentacles have per- 

 sisted. In the medusa form which has become secondarily free,. 



