CTENOPHORA. 



35 



consideration of such a form as Ctenopland'\ Willey claims to have proved conclusively that the 

 tentacle axis of Cfciiop/aiia corresponds to the longitudinal axis of the flat-worms. But Ctrnoplaiin, 

 when creeping, has not one of the tentacles directed forwards, it creeps with one side foremost, viz. 

 after the sagittal axis. Heteroplana moves "in a somewhat one-sided fashion, and the number of mar- 

 ginal eyes on the forwardh- directed lobe is more than twice that on the corresponding lobe on the 

 opposed side of the frontal region". Heteroplana "is almost directly derivable from a biradial type of 

 the same grade of organisation as Ctenoplana. But in Heteropla)ia the direction of locomotion (creeping) 

 has been definitely localized, and the side (namely the right side) to which the preference has been 

 given has for that very reason predominated over the other (left) side. In other words, in Heteroplana 

 there is hypertrophy of the right side and atrophy of the left". 



Instead of entering on a discussion of Wil ley's profound reflections on the relations of sym- 

 metry I will only give a reproduction of the .sketch of Heteroplana given by Willey (Fig. 9). Is not 

 the only reasonable explanation of the figure this, that it represents a Planarian which has, in some 

 way or other, lost the left half of its bod\- and is now about to regenerate it? The fact that 

 Willey did not find more than one specimen is certainly not against such an explanation. Herewith 

 I think we may safely leave this animal out of the discussion. 



Gastrodes parasiticum Korotneff there is no reason to dis- 

 cuss here, its affinities to other Ctenophores being quite obscure; *^ 

 I think it would be hard to find any special relation between it and 

 Tjalfitlla. The question about the systematic affinities of Gastrodes 

 can upon the whole scarcely be solved before its development has e'' 

 been studied. 



Having thus critically examined the different forms of real or 

 supposed, aberrant Ctenophora and pointed out how far they show q,_ . 

 structural resemblances to Tjalfiella, the question remains whether 

 perhaps a nearer relation can be shown to exist between any of the ; ,•<- 

 groups of typical Ctenophores and Tjalfiella. This question must, I 

 think, be answered in the affirmative. 



Taking first the Beroids, it must be conceded that the well 

 known proliferations from their meridional canals in some way remind 

 one of the branching peripheral canals in Tjalfiella (and Coeloplana 

 and Ctenoplana). Further the peculiar development of the polar plates 

 of Beroe^) recalls the condition found in Ctenoplana, as pointed out pi^, ^ Heteroplana Newtoni WiUey. 



by Willey (Ctenoplana p. 332). However, the presence of tentacles (From Willey. Op cit) e. eyes; I. i. 



"left rudiraentarj' intestiual diverti- 

 in Tjalfiella shows beyond doubt that it has no real relations to the cula"; o. position of mouth on ventral 



Beroids; it is needless then to point out the other characters in whicli ''''^^^^' r.i. right intestinal diverticula. 



they differ from each other. The resemblance in the branching canals of the gastrovascular system are 



merely a superficial analogy, as is also the resemblance between the polar plates of Ctenoplana and Beroc. 



') Perhaps not found in all Beroids; it remains uncertain whether the species of the genus Pandora have the polar 

 plates thus developed — in any case P.mitrata Moser appears to have simple polar plates. Moser, Japanische Ctenophoren. 

 .\bh. Bavr. .\kad d. Wiss. 1. Supjjl. 4. 1908. p. 35. (Beitr. z. Naturgesch. Ostasiens, herausg. v. Doflein). 



5* 



