STRUCTURE AND DFA'FJ.OPMENT OF CnET.OPTANA. 69 



pharynx which appears in the advanced stage of the larva and which 

 leads to the production of the flattened shape of the adult. And, what 

 seems to be the most important, is that, this way of the production of 

 the flatness and dorsiventrality of the body of Cocloplana is entirely 

 different from that which brings about the same feature of the body of 

 the Turbellaria — while in the former, that results from the out-opening 

 of the lower part of the pharynx, in the latter, according to Lang ('84), 

 it is due to the bending of the principal axis of the larval body towards 

 the anterior direction and by the concomitant growth of the body in 

 the plane perpendicular to the original vertical axis. Thus, the facts 

 about development apparently point to the conclusion that, the close 

 resemblance of Coeloplana to turbellarians in several structural features 

 has developed mainly by the converging evolution of the two forms and 

 can not be taken as evidence of the former standing phylogenetically 

 close to the latter. Besides this fact, if the Turbellaria has developed 

 from the Ctenophora, it seems to be improbable that the former has 

 arisen from a highly specialized form of the latter; it is by far more 

 natural to assume that the Turbellaria has developed from an ancestral 

 and less specialized form of the Ctenophora. But, it must be admitted 

 as well that, in spite of the fact mentioned above, the actual existence 

 of such a form as Coeloplana among the Ctenophora affords a strong 

 suggestion as to how an ancestral ctenophore might have changed into 

 a turbellarian, as it has been pointed out by Korschelt & Heider ('90) 

 and Bourne ('00). 



Summary. 



(i). Coeloplana is represented in the waters of Misaki by three 

 distinct species, namely, C. willeyi Abbott, C. mitsukurii Abbott and 

 C. bocki KoMAi, of which the anatomy was studied in all the three, and 

 the development in the last-named species. 



(2). The epidermis is the same in structure as in ordinary 

 ctenophores, consisting of gland cells and interstitial cells; of the gland 

 cells, two kinds, the clear and the granular, may be distinguished. In 

 the epidermis of the ventral side, the interstitial cells are replaced by 

 ciliated cells. 



(3). The aboral sense-organ is nearly identical with that of 

 ordinary ctenophores; in C bocki, the margin of polar plates is divided 

 into some lobes. 



