CTENOPHORA. 



While it would scarcely be possible to point out other resemblances between Tjalfiella and the 

 Cestidse than those necessarily following from the fact that both are Ctenophores, the case is different 

 with the Lobatse ( including the Ganeshidse ). On comparing the young Tjalfiella in the Cydippid- 

 stage with a young Lobate, we find a conspicuous resemblance in the oral lobes, thotigh they are not 

 quite so early developed in the Lobatae (in any case in Eucharis inulticornis and Bolina infundibulu/n, 

 the only two forms whose development has been studied more closely as yet). Further the shape of 

 the aboral side of the young Tjalfiella resembles that of the young Lobatse, and in both the aboral 

 organ is more or less sunken. These points of resemblance can certainly not be done away with as 

 being merely cases of analogy, the more so as they occur in the young stages only; they might well 

 be regarded as indicating a real relation between these forms. On the other hand the very great 

 difference in the gastrovascular system shows that the affinity cannot be so very close; the two 

 groups may have originated from a common source, but they have then developed further 

 along very different lines. Bourne, to be sure, thinks that the peripheral canals of Ctenoplana may 

 be compared with the canals of the lobes of Lobatae, which would then also apply to Tjalfiella (Op. 

 cit p. 17). With this, however, I can not agree. The canals of the lobes of Lobatae represent only 

 prolongations from the meridional canals, which reach their highest perfection in this order; in 

 Tjalfiella and the two allied forms, Ctenoplana and Coeloplana, there are no meridional canals at all, 

 the peripheral branching canal being outgrowths directly from the large interradial lobes. - 



It remains to examine the possible relations between Tjalfiella and the Cydippidae. The fact 

 of the young Tjalfiella being a typical Cydippid undoubtedly shows that its ancestors, like 

 those of all the other tentaculate Ctenophores, were Cydippids, and more especially forms 

 like the Mertensiidae, having the tentacle axis longer than the sagittal axis. This suggestion is con- 

 firmed by the most interesting deep-sea Ctenophore recently described by Moser 1 ) under the name of 

 Mertensia Chuni. This remarkable form has a pair of oral lobes recalling very much those of the 

 young Tjalfiella, being in the same position and very much of the same form. The polar plates are 

 small. Further it has a rich net of branching canals from the pharyngeal vessels, and also from the 

 meridional vessels fine proliferations arise; finally the inner wall of the pharynx is closely covered 

 with hollow, partly ramified "Zotten" 2 ). Though the branching canals can scarcely be directly com- 

 pared with those of Tjalfiella, it is evident that this form among all the typical Ctenophores made 



') Die Ctenophoren der deutschen Siidpolar-Exped. Deutsche Sudpolar-Exp. 1901 1903. XI. Bd. Zoologie Bd. III. 

 1909. p. 126 130. 



2 ) It seems very remarkable that Dr. Moser has referred this peculiar deep-sea form to the genus Mertensia. The 

 only species of the genus Mertensia hitherto known, M. ovum (Fabr.), has certainly never been fully described, or adequately 

 figured (the beautiful figure given by Torrey in his Ctenophores of the San Diego Regiou (Univ. Calif. Publ. Zool. Vol.2, II. 

 1904. PI. I. Fig. i) under the name of Mertensia ovum is certainly not that species, as pointed out by Moser (Op. cit. p. 126)) 

 but so much is known, however, that it has no oral lobes and no proliferations from the pharyngeal vessels (perhaps there 

 are such on the meridional vessels; comp. the remarks on M. ovum in Part II of this memoir); further the tentacle sheaths do 

 not open orally as in the deep-sea form and still other differences might be pointed out. That the deep-sea form repre- 

 sents a very distinctly characterized genus seems to me beyond doubt. I may propose the name Bathyctena n. g. I do not 

 even feel certain that it can remain in the family Mertensiidae, but on a discussion of this question I shall not enter. By 

 the way, I may further be permitted to make a little remark on account of the description of M. Chuni. Dr. Moser suggests 

 that the thick pharynx walls and the reduction of the lumen of the pharynx, the strong lips which are able to close the 

 mouth tightly, the narrow tentacle sheaths and the position of their very small openings at the oral, instead of at the aboral 

 pole as is otherwise the rule, are special adaptations to the life in the deep-sea which "befahigen . . . den kolossalen Druck des 

 Wassers und dessen Eindringen in ihre Korperhohlen einem grosseren Widerstand zu leisten". This suggestion can scarcely 

 be right -- the idea that a jellylike animal could upon the whole make any resistance to the pressure of the water in a 

 depth of ca. 3000 in seems not very probable, even if the jelly is ever so resistent. 



