PREVIOUS INTERPRETATIONS OF CNIDARIA 159 



into thcAnlagen of special sex individuals; these finally develop 

 into independent freely swimming individuals, into the second 

 generation. 



In this the Hydrozoa resemble the Scyphozoa, with 

 the only difference that in the Hydrozoa the medusoid 

 generation does not develop by way of a transverse divi- 

 sion but rather by way of lateral budding so that they 

 are therefore further developed from an independent root. 

 We can observe, moreover, in Hydrozoa a secondary disap- 

 pearance of the primary polyp generation and the prevalence 

 of the secondary medusa form, hypogenesis (Trachylina), 

 without a development of special auxiliary sex organs. 



It is clearly in connection with this that in Hydrozoa the 

 second sexual medusoid generation develops from "heads" 

 of polyps (hydranths) which had been developed by 

 way of budding, on the bearer of these polyps. This has 

 frequently led to further complications. The colonial or 

 cormus state which made it possible that those zooids in which 

 the budding of medusae takes place, abandon their normal 

 feeding function and develop into pure bearers (which are 

 without tentacles and without a mouth) of medusae or of 

 reduced medusae— of gonophores. They have been given a 

 special name, that of a blastostyle. This again has led to a 

 polymorphism (e.g. Fodocorjne carnea). It is frequently difficult 

 to determine whether we have in a certain case a strongly 

 retrogressed polyp type bearer of gonophores or whether 

 we have perhaps a special form, e.g. a stem of a bud 

 (Fig. 30). 



Frequently the development does not stop here, and an 

 even greater influence can be exerted in a cormus by the 

 Anlage of a gonad upon its whole environment. Thus in the 

 case of Aglaopheniidae, among the Thecata, where medusae 

 had become strongly retrogressed and where they remain 

 attached to the cormus, we can observe the transformation 

 of a whole branch of the cormus together with its minute 

 twigs so that they form a protective receptacle around the 



