S'l'RUCTURE AND DEVELOPMENT OF COELOl'LANA. 65 



Ctcnoplana and Coeloplafia 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 A 



necessary conclusion from the close affinity between Ctenophores and 

 Polyclads would seem to be, that the Ctenophores 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" ('12, p. 58)- 



But regarding the problem on the homology of the ventral surfaces 

 of Coeloplana, Ctenoplana, Tjalfiella and polyclads, he seems to be of 

 an opinion differing not only from all the previously named authors 

 but also from Lang. Thus he gives: — "While Lang appears to think 

 the flat shape of the polyclads the result of a simple shortening of the 

 main axis, the edge of the Planarian body thus corresponding to the 

 equatorial zone of the Ctenophoran body, Hatschek (Lehrbuch der 

 Zoologie, p. 319) points out that Coeloplana and Ctenoplana ' wahrschein- 

 lich nicht mit der aboralen Flache kriechen, sondern mit dem ausgebreite- 

 ten Schlunde, wie dies auch andere Ctenophoren gelegentlich thun '. 

 Likewise K. C. Schneider regards the flat oral side of Coeloplana and 

 Ctenoplana as homologous with the lower part of the pharynx of other 

 Ctenophores, the well known Lampetia pancerina Chun, which even 

 uses the inverted pharynx for creeping, being taken as the proof of the 

 homology.— The morphology of Tjalfiella and Ctenoplana decidedly gives 

 no support for this theory. It is the transverse furrow which becomes 

 the flat underside, in the middle of which is the opening of the pharynx. 

 In Lampetia there is no trace of a transverse furrow, the eversion of 

 the sagittally compressed pharynx being morphologically quite a different 

 thing, though it may physiologically serve the same purpose, viz. to 

 form a flat surface adapted to perform creeping movements" (the same, 



p. 56). 



Now, after finishing the review of the opinions hence put forward 

 concerning the systematic position of Coeloplana, let us consider how 

 the facts given in the foregoing pages may throw light on the same 

 problem. First of all, I may give the undeniable conclusion drawn from 

 the study on the structure and development of this animal that, the 

 evidence is indubitably in favour of the view that, first, Coeloplana is 

 nothing but an extremely specialized ctenophore, adapted to the creeping 

 mode of life, instead of to the pelagic habit, and second, the flatness and 



