PREVIOUS INTERPRETATIONS OF CNIDARIA 



161 



pretation is the suggestion which I have already proposed in 

 one of my studies (Hadzi, 1954), i.e. that the Siphonophora 

 had evolved from the sessile cormi of the athecate Hydroidea 

 by way of a transition to a life in plankton; they therefore 

 represent an order of very polymorphous individuals partly 

 of a polypoid and partly of a medusoid character. In all 

 cases the basis of the cormus is an impersonal stock (siphono- 

 some) which corresponds to the hydrocaulus of the Hydro- 

 idea. The orientation of the cormus had been turned similarly 



Fig. 31. Two examples of gonosomas of the hydroids. A, corbula 

 of Aglaophenia pluma and B, coppinia of 'Lictorella pinnata; (after 



Broch). 



as in the case of medusae. In part of the Siphonophora (Pneu- 

 matophorae Chun 1897 or Siphonanthes) we can find at the 

 root of the stock which can secondarily be flattened and 

 which can resemble externally a medusoid form, that a pneu- 

 matophore had been developed as an organ of the cormus and 

 it therefore does not correspond to a medusoid individual. 

 The Calycophorae (Leuckart 1854) and Pneumatophorae (Chun 

 1987), the two suborders of the Siphonophora, had separated 

 phylogenetically quite early so that the species belonging to 

 the first subgroup had not developed their own pneuma- 

 tophore (or is it possible that they had originally possessed 

 it and had lost it only subsequently?) and they use as their 

 hydrostatic and swimming apparatus, the more or less modified 

 swimming medusoids only. The Disconanthes are the most 

 specialized subgroup of the Pneumatophorae. 



