OS T. KOMAI: STUDIES ON TWO AllERRANT CTP:NOPHORES 



also that, its flatness and dorsi ventral ity has resulted from the out- 

 spreading of the external part of the pharynx. But there should remain 

 the question to be answered on the affinity of the form to the Turbel- 

 laria, that is, whether Coeloplaiia does represent an intermediate stage 

 in the evolution of the Turbellaria from the Ctenophora, or whether its 

 resemblance with the former group is nothing more than an instance of 

 the phenomenon of converging evolution. Before entering upon this 

 question, I shall enumerate the following points regarding which Coelo- 

 plaiia is departed from the ordinary Ctenophora and approaches the 

 Turbellaria : 



(i) the creeping mode of life, 



(2) the flatness and dorsiventrality of body, 



(3) the absence of comb-plates, 



(4) the presence of pigment, 



(5) the presence of an extensive ramifying gastro-vascular 



canal-system, 



(6) the presence of powerful muscular system, 



(7) the division of male gonad into some compact sperm masses. 



(8) the presence of a duct to each sperm mass, 



(9) the presence of seminal receptacles. 



It can not be denied that, on account of the presence of these 

 features, the resemblance of Cocloplana to the Turbellaria is very striking. 

 Nevertheless, it would be hasty to conclude from this fact alone that 

 Cotloplana stands phylogenetically between the Ctenophora and the 

 Turbellaria, because, all of the above features, in my opinion, can as 

 well be regarded simply to have arisen in relation with the peculiar 

 creeping habit of the animal, thus, taken together with the similar 

 characteristics of the Turbellaria, affording only a fine instance of the 

 phenomenon of converging evolution. Indeed, each of those features 

 can be accounted for equally well by assuming either of those two 

 hypotheses, and this shows that it is difficult to settle this question by 

 the anatomical data alone. So, naturally, our attention is directed to 

 the facts about development. It is probale that, should Coeloplana be 

 really a form standing phylogenetically between the Ctenophora and the 

 Turbellaria, its development would show some deviation from that of 

 the Ctenophora in general and approach as much to the development 

 (jf the Turbellaria. 1 hnvever, as a matter of fact, the development of 

 Cocloplana is identical with that of ordinar)' ctenophores in every detail, 

 e.xcept for that peculiarity in the condition of the oral aperture and 



