NEW INTERPRETATION OF CNIDARIA 231 



sist of two body layers only; (3) they have developed their own 

 medusa form, the hydromedusa, which is formed primarily by 

 way of budding (and secondarily directly from the egg cell) ; 

 secondarily the medusa generation is frequently more or less 

 reduced ; (4) only they have developed pelagic, polymorphous 

 (also with regard to the medusa form), and strongly individua- 

 lized cormi (Siphonophora). 



Changes that have occurred within the frame of individual 

 groups (subclasses, earlier classes) must also be studied 

 in agreement with this new interpretation of the phylogeny of 

 Cnidaria; they cannot, however, be discussed here in greater 

 detail. As for Anthozoa, we can preserve their present sub- 

 division into two groups of Hexactiniaria (Hexacorallia) and 

 Octactiniaria (Octocorallia), yet with the difference that, in 

 contrast to the present sequence, we give Hexactiniaria the 

 first place, and Octocorallia the second. This is not difficult to 

 justify. The polymerous state with large and not fixed numbers 

 is, according to a very generally valid rule, the primitive state, 

 and the oligomerized state with a fixed and diminished number 

 is secondarily developed from the former. We must therefore 

 reverse the presently valid sequence and put Hexactiniaria into 

 the first place and Octactiniaria into the second place. Other 

 properties of these two groups also agree wdth this new 

 sequence. Thus we find, for example, the primarily solitary 

 anthopolyps (among these a type with a rounded off aboral 

 end) among the Hexactiniaria only. A dimorphism of polyps 

 and the individualized cormi can be found in Octactiniaria 

 only. Octactiniaria each have (with one exception where 

 we find a different number of septa) eight branched tentacles. 

 Hexacorallia have been given the first place also by some other 

 zoologists (e.g. A Kastner, in his 'Lehrhmh der spet(iellen Zoo- 

 logie, yet he does not give his reasons for such a sequence). 



It is clear that the first order within the gtoup Hexacorallia 

 is that of Actiniaria. This has usually been the case in earlier 

 classifications, too. As for the remaining orders, we find the 

 equally primarily solitary Ceriantharia regularly placed at the 

 16* 



