NEW INTERPRETATION OF CNIDARIA 



241 



place is given to the first or to the second group. It was a retro- 

 grade step in the classification of Hydrozoa when the accepted 

 rank of order was given to two families by Hyman in spite of 

 the fact that this classification has now been found to be 

 erroneous; to Stylasteridae (they are valued by Stechow only as 



Fig. 45. A few secondarily solitary hydropolyps. A, Hydra sp. 

 B, Protohydra sp. C, " Microbydra" -polyp of Craspedacusta sp.: D. 

 ^^Haleremita" -polyp of Gonionemus sp. (after various authors.). 



a subfamily), and to Milleporidae (which have also been degra- 

 ded by Stechow to the rank of a subfamily). 



In spite of the fact that from our viewpoint there can be no 

 doubt that the Hydrozoa had inherited their tendency to 

 alternation of generations from their scyphozoan ancestors, 

 it seems nevertheless more probable that the ancestors of the 

 present Hydrozoa had separated from the ancient Scyphozoa 

 before the latter had developed their own medusa generation. 



