230 THE EVOLUTION OF THE META7.0A 



in the middle between Anthozoa and Hydrozoa. Theoretically, 

 a third type of evolution is also possible, i.e. that all the three 

 subtypes of the Cnidaria had developed in parallel, from a 

 hypothetical indifferent state. Such a concept, however, seems 

 to me as completely improbable. As for the classification 

 however, it is irrelevant which of the possibilities be true. It 

 appears as very probable, in view of the great difference which 

 can be found in the way that the medusa form is primarily 

 developed from the primitive polyp form in the two groups 

 of Cnidaria, that the separation of both Scyphozoa as wxll as of 

 Hydrozoa took place at a time when neither the former nor 

 the latter had yet developed their medusa forms. 



The main characteristics of Anthozoa can be enumerated 

 as follows: (1) they have a muscular gullet (pharynx 

 with siphonoglyphs (2) they have primarily solitary in- 

 dividuals (3) they have a polyp form and no medusa form; 

 (4) they have w^ell-developed longitudinal folds in their 

 intestine, the genuine sarcosepta which are orally connec- 

 ted with the gullet; (5) they form intracellular sclerites which 

 are permeated with the calcium carbonate; (6) they still have 

 a well-developed middle layer. 



The following elements are characteristic of Scyphozoa: 

 (1) their "septal apparatus" is strongly reduced in the form of 

 usually four short taeniolae with taeniolan muscles and 

 teaniolan funnels; (2) they have developed scyphomedusae as 

 a special sexual generation which has become the predominant 

 form of Scyphozoa or even a form which alone has been pre- 

 served (the hypogenetic species); (3) they do not possess an 

 ectodermal gullet; (4) scyphomedusae are developed, with the 

 exception of the hypogenetic species, w^here they develop 

 directly from the egg and the lanal cells, from polyps by way 

 of a transverse division. 



The following characteristics should be mentioned in con- 

 nection with Hydrozoa: (1) no traces of sarcosepta or pharynx 

 can any longer be found in their polyps; (2) their middle layer 

 is strongly reduced so they give the impression that they con- 



