CTENOPHORA. 



25 



regenerate even unimportant parts removed from their body. In his famous memoir "Die Dissogonie" 

 (p. 103) Chun even more definitely states that "den Ctenophoren nach den tibereinstimmenden Berichten 

 aller Beobachter ein Regenerationsvermogen abgetrennter Theile durchaus abgeht". That this is, how- 

 ever, not an unexceptional rule, is proved also by the facts recorded below of Bolina infu7tdibulum. 

 This Ctenophore I have found to be in possession of even quite a remarkably great regenerative 

 power. Also Beroe aiatmis appears to be capable of regenerating large and important parts of the 

 body, though I have made no direct experiments with this form. From this I would be inclined to 

 think that Chun is not right in his statement, it seeming rather singular that the Bolina .should 

 differ so conspicuously from other Ctenophores (except Tjalficlla) in this respect. 



D. Affinities of Tjalfielia. 



Turning now to the question of the relations of Tjalfielia to other Ctenophores, the atten- 

 tion is naturally first directed towards the other aberrant Ctenophores known, viz. the two genera 

 Ctenoplana and Coeloplana, constituting the order Platyctenida. 



It is easily seen that there are several points of resemblance between Tjalfielia and Ctenoplana. 

 The costse are deeply sunk in Ctenoplana as in the young Tjalfielia. According to both Korotneff 

 and Willey the costse of Ctenoplana dire withdrawn by means of a specially developed muscular system; 

 as it is shown below that the peculiar muscular system ascribed to Ctenoplana by Korotneff and 

 (partly) by Willey is nothing but the tentacle, withdrawn into the sheath, it becomes very improb- 

 able that such special retractor muscles of the costae really exist. The fact that the young Tjalfielia 

 has its costse sunk in a similar way (without being retracted by muscles) would seem to indicate that 

 it is also their natural position in Ctenoplana. I would suggest that the supposed retraction is only 

 the lying down of the combs, when swimming is interrupted. — Korotneff's suggestion (Op. cit. p. 250) 

 that the combs of Ctenoplatia have lost their function as swimming apparatus and become "ein Schutz- 

 apparat, wie die Borsten der Anneliden" is, of course, refuted by Willey's direct observation of their 

 being used in the usual way. 



A feature specially worth mentioning is that Ctenoplana can fold itself up in the transverse 

 plane, having thus two large lobes, which it can open or lay together, just as is the case in the young 

 Tjalfielia. 



Also in the structure of the gastrovascular system there is a considerable resemblance between 

 the two forms. As seen from the figure 3, (p. 26), copied from Korotneff, there is a pharyngeal cavity 

 with richly developed folds as in Tjalficlla. Korotneff regards this cavity as the stomach, the folds 

 being regarded as "Darmaste" (Op. cit. p. 241). The oesophagus and infundibulum are mainly alike 

 in both forms; both have a richly developed branching peripheral gastrovascular system (anastomosing 

 in Ctenoplana, not anastomosing in Tjalfiella\ and both lack the meridional canals. — On the other 

 hand there would appear to be also some very essential differences in the gastrovascular system. The 

 branching peripheral canals are stated by Korotneff to arise from the folds of the pharyngeal cavity, 

 while according to Willey (p. 328) "the two end-lobes are in open communication with the peripheral 

 canal system". There can certainly be no doubt that the observations of Willey regarding this 



The Ingolf-Expedition. V. 2. 4 



