CTENOPHORA. 



59 



have been raised as well as those which are affected by the facts brought to light by the more 

 recent researches on Ctenoplana and Coeloplana and, especially, those here recorded on Tjalfiella, we 

 may state as the main result that all the new facts are decidedly in favour of the theory, 

 which now seems thus strengthened that serious objections can scarcely be raised against it any more. 

 It seems to be an established fact that we can here really follow the transformation of the 

 radiate into the bilateral type. The main point in this transformation lies in the 

 relations of the main axis. After having been shortened through the flattening of 

 the aboral side of the body it becomes bent through the wandering forwards of the 

 apical pole, while the oral pole still remains in the middle of the under side. At the 

 same time it becomes considerably shortened through the splitting up, along the 

 transverse plane, of the oral half of the body. By the folding out of the lobes the flat 

 underside is formed. The sagittal and transversal planes of the radiate body pass 

 directly into the sagittal (vertical, longitudinal) and transversal planes of the bila- 

 teral body; the latter, of course, must be bent parallel to the main axis. Secondary 

 changes of the axial relations are then introduced by the wandering forwards (or backwards) of the 

 oral pole. But there is no reason to enter on the further development of the bilateral type. It may be 

 sufficient to have demonstrated how the transformation from the radiate to the primitive 

 bilateral type has been brought about 



A necessary conclusion from the close affinity between Ctenophores and Polyclads would seem 

 to be, that the Cteuophores ought to be classified with the Platyhelmia instead of with 

 the Coelenterates, their affinities with the latter being, indeed, rather problematical, or, in any 

 case, much less conspicuous than those with the Polyclads. I must, however, refrain from discussing 

 this question on the present occasion, the more so as it cannot be done with due weight, before 

 Coeloplana has been studied more fully in regard to both its anatomy and its development 



8* 



