2 T. KOMAI : STUDIES UN TWO AliERKANT CTENOPHORES 



INTRODUCTORY. 



Although Abbott's works on Coeloplana which appeared in 1902 

 and 1907 shed a great deal of light on the structure of that interesting 

 animal, yet much has remained to be elucidated, especially as regards 

 its development. In fact, the embryology of the animal has never been 

 studied. As a consequence, there still exists a difference of opinion 

 among authors with respect to the systematic position to be assigned 

 to the animal, some of them regarding it as a transitional form in the 

 stages of evolution from the Ctenophora to the Turbellaria, while others 

 believe its striking resemblance to the latter group to be nothing more 

 than an instance of convergent adaptation. 



In 19 1 6 I took up the study of Coeloplana with the intention of 

 verif\^ing the accounts given by Abbott and to fill up, if possible, some 

 of the gaps in our knowledge of the animal. Fortunately enough, 

 a fairly plentiful supply of material for my use could be obtained 

 at Misaki. This enabled me to realize my intention in a measure. 

 Especially a fortunate circumstance was that material was securable on 

 which to undertake a study of the development. Some of the results 

 of my lesearches have already been given in a preliminary report 

 published in 1920 (a). The present paper embodies a fuller account of 

 the results in regard to the anatomy and development of the animal. 



During the whole course of the study, I was quite unaware of 

 that Krempf also had been engaged in the same research. But, when 

 I saw his work published, I was glad to find that, there was no great 

 discord between our studies, at least as far as important points are 

 concerned. I have been able to refer to his results in the present work, 

 and as to the points of disagreement, I have dealt with them somewhat 

 in detail. 



The facts about Gastrodcs given in the second part of this paper are, 

 so to speak, by-products of the research in Coeloplana. While consulting 

 literature necessary for that work, my attention was attracted to the 

 existence of another peculiar form called Gastrodcs which had been 

 referred to the Ctenophora with some doubt, and in the hope of 

 making out the nature of that animal, I was waiting for the opportunity 

 of studying it. And it was again my good luck that a plenty of 

 materia! was obtained s(;on afterwards at Misaki and enabled me to 

 ascertain without difficult}^ that the animal is unmistakably a ctenophore 

 and moreover a form most probabl}' referable to the group Platyctenea 



