160 



THE EVOLUTION OF THE METAZOA 



"gonangia;" this is called a corbula because of its similarity 

 with a basket. Simultaneously the polypoid individuals have 

 been strongly modified and they have become in this way 

 polymorphous. It was originally thought that this w^as a case 

 of other species living epizoically on the cormi of Hydroidea, 

 and for this reason these groups of accumulated gonophores 

 and of transformed other zooids have been given special 



Fig. 30. Reduction of hydropolyps as bearers of gonophores. A, 

 Podocoryne carnea {after Brooks). B, Endendriiim sp., (from Hyman); 

 C, gonangium of Gonothyrea sp., with gonotheca, blastostyl and 

 medusoid-buds (after Hyman). 



names, e.g. Coppinia in luafoea pygmaea Alder (Hebellidae), or 

 Scapus in 'Lictorella pinnata (Fig. 31). 



In the Hydrozoa the Siphonophora form an interesting case. 

 Contrary to the recent attempts made by A. K. Totton (1954) 

 to separate part of the Siphonophora-Disconanthes or Chond- 

 rophora from the remaining Siphonophora and to establish 

 them as a special taxon, I am of the opinion that the Siphono- 

 phora had evolved monophyletically and that they must 

 therefore be considered as an indivisible unit, i.e. as an order 

 of the Hydrozoa. The old discussion on how to interpret the 

 organisation of the Siphonophora and their origin has not 

 come to an end yet, still I think that the most probable inter- 



