90 THE EVOLUTION OF THE META20A 



into a sessile hydropolyp. It is in the Trachylinae only whose 

 hypogenetic character is a secondary phenomenon because 

 they have secondarily lost their polyp generation (which had 

 been their first and primitive generation) that a polypoid 

 larva had been developed due to their adaptation to the life 

 in plankton. The evolution of this truly polypoid larva of 

 Trachylinae has been— in connection with its parasitism— pro- 

 gressive and it led finally to a new asexually produced genera- 

 tion. 



The rigid adherence to a wrong interpretation of the polyp 

 form in general— and not of Trachylinae only as secondary 

 larval forms— has induced Hyman to the following absurd 

 conclusion, "The hydroid colony thus represents a persistent 

 larval state." In the same way we could be justified to call 

 the medusoid form a persistent larval form of the polyp. Hyman 

 believes that "something like the present actinula larva" 

 was the universal starting point even of Siphonophora, and 

 this was, at a very early point. The Scyphozoa, which could 

 be explained even more easily as exclusively medusoid forms, 

 have been evolved, according to Hyman, from the Trachy- 

 linae. The Anthozoa, the third subtype of Cnidaria can then 

 be easily deduced from a scyphistoma which is, naturally 

 enough, again a larvoid form. It is surprising how Hyman 

 acknowledges, and this without any explanation, that in 

 these, "all trace of the medusa is lacking." 



The interpretation which considers the medusa form to be 

 the primary form can be defended only if we accept the 

 proposition that the phylogenetic development of Cnidaria 

 began with the Hydrozoa and that it was progressive 

 because no medusa can be found in Anthozoa. This proposi- 

 tion has been generally defended as the correct interpretation. 

 Yet even if we disregard this we can find facts which support 

 the idea of the primacy of the polyp form. We have here, 

 besides others, the fact that medusae develop regularly out 

 of polyps; in those cases w^here a medusa is developed directly 

 out of its egg— a phenomenon which has been given a special 



