NEW INTERPRETATION OF CNIDARIA 



237 



to which had been prepared as early as in Anthozoa, finds its 

 climax in the Siphonophora. 



It was in agreement with the old interpretation which believ- 

 ed in a progressive evolution of Cnidaria, that within the 

 Hydroidea, the Athecata w^ere considered quite generally and 



Fig. 44. The progressive and regressive evolution of the hydro- 

 thecae. A, Hebella sp. B, L.afo'eina vilae-velehiti Hadzi, with oper- 

 culate hydrotheca; C, Haleciella microtheca Hadzi. D, Halarithus 

 adriaticus Hadzi, the theca has fully disappeared, and remains only 

 as the tonofibrilles. E, Hiigymnantha inquilina Palombi, a "thecate 

 hydroid" without the rest of periderm (A-D after Hadzi, E, after 

 Palombi). 



without exception in comparison with the Thecata, as the 

 more primitive initial group. It was considered that since 

 Athecata have simpler forms that they must also be the more 

 primitive animals; at the same time soHtary species, and above 

 all Hydra, have been known as Athecata. There are no really 

 solitary Thecata, close to this state is only the species 'Eu- 

 gymnantha inquilina Palombi (Fig. 44). Furthermore, it is 

 known that the cormi of Thecata show a higher degree of 

 individualization than those of Athecata. Because of the new 



