PREVIOUS INTERPRETATIONS OF CNIDARIA 109 



are, however, numerous species where the polyps have al- 

 ready become solitary individuals, yet with a periderm which 

 they have still preserved as their external skeleton; the peri- 

 derm must be interpreted as a remnant from the former for- 

 mation of colonies; in numerous other species the scypho- 

 polyps are completely "naked," i.e. they have no periderm, yet 

 in spite of this they still continue to reproduce by way of 

 budding or by means of the formation of stolons. In not one 

 single case in the Scyphozoa has polymorphism been deve- 

 loped. 



Polymorphism Has Reached Its Climax in Hydrozoa 



Polymorphism (dimorphism when it is least developed) in the 

 cormi of polyps is another piece of evidence which supports 

 our thesis. It is a sign that a higher stage in evolution has 

 been reached when this polymorphism appears in combination 

 with the individuaUzation of the cormus (colony). In the 

 Anthozoa the dimorphism of polyps has been developed among 

 the Octactiniaria only, a fact which can again be considered 

 as a proof of their higher condition in comparison with 

 Hexactiniaria. Siphonozooids, whose number has been rather 

 reduced, appear either in species that form irregular cormi, e.g. 

 in the red coral (Corallium ruhrum L.), or in species with regu- 

 larly, and thus individually, formed cormi e.g. Pennatulacea. 

 No cases of polymorphism have been known in the Scypho- 

 zoa and this can be easily understood since they form, with 

 a few exceptions, no cormi. 



The highest level in differentiation, and thus of specializa- 

 tion, has been reached in the Hydrozoa, a clear indication 

 that in them the Cnidaria have reached a climax in their 

 evolution. In these polymorphism can even be found in 

 the medusoid form, i.e. in the mixed polypo-medusoid cormi of 

 Siphonophora that Hve in plankton, with a simultaneous in- 

 dividualization of cormi. Nothing similar can be observed in 



