STRUCTURE AND DEVELOPMENT OF COEEOPLANA. 6r 



apparatuses and four on each side of the sagittal plane, just as in that 

 form. This fact seems to stand in favour of the opinion of the present 

 author on the systematic position of Gastrodcs, that the form should be 

 assigned to the Platyctenea. 



Systematic position. 



Since its first discovery made by Kovvalevskv in 1880, Coeloplana 

 has often been regarded as a form which occupies a very peculiar 

 s\'stematic position. This is because the animal possesses several 

 features common with flatworms on one hand, while showing many 

 other characteristics standing for its affinity to ctenophores on the 

 other. In fact, this peculiarity has not failed to attract the discoverer's 

 attention, notwithstanding that the form was then represented by an 

 unique specimen. The Russian zoologist pointed out so ably that : — 

 " As to the systematic position of Coeloplana * we know too little to 

 decide it at present; especially do I feel it necessary to examine an 

 individual that has attained maturity. Nevertheless, so far as I could 

 ascertain, it may be pointed out, among other facts, that the animal 

 shows affinity to the Turbellaria on one hand and to the Ctenophora 

 on the other. It approaches the Turbellaria in its general habitus and 

 life habit, whereas, such features as, the situation of the mouth and 

 otocyst at the centre of the body with the latter above the former, the 

 existence of two diverticula projecting from the intestinal canal and 

 terminating on the sides of the otocyst, the presence of tentacles and 

 their sheath, and further, the division of the intestinal cavity into four 

 primary parts, show the relationship of the animal with the Turbellaria " 

 (Translated from Russian with Professor A. Oka's kind aid). 



Two years after this discover}-, Lang (1882) published a brief 

 remark on the systematic position of Coeloplana apropos of the description 

 on the structure of Gtinda and the argument on the relationship of the 

 Plathelminthes with the Coelenterata and Hirudinea. Of his great work 

 on the Neapolitan Polyclada published still two years later (1884), the 

 same author devoted its concluding chapters to his well-known theory 

 on the affinity of the Turbellaria with the Ctenophora, and he has 

 attempted to derive the former class from the latter by taking Coeloplana 

 as an intermediate form between the two. He has described in detail 



* uiij^inally spelt '■'■Cocle^land'. 



