PLANKTON FROM NEW BRUNSWICK. 289 



parallel with the axis of the mouth and polar sensory field. The 

 two pairs of ciliated auricles are a distinctive feature of Bolina. 

 The auricles and the reduced inconspicuous tentacles between 

 them occur on either side of this extended pallial axis. When 

 seen from the aboral aspect, as fig'ured by Agassiz, with the lobes 

 flattened out, the organism exhibits a pronounced biradial sym- 

 metry, the mouth-cleft and the polar field being parallel to one 

 another in the direction of the longer axis, which coincides with 

 the plane of the flattened stomodteum, whence it is called the 

 stomodfeal axis. 



In his memoir on Pleurohrachia, Agassiz, in spite of some 

 textual confusion, clearly considered the stomodseal axis to cor- 

 respond with the sagittal axis of bilateral animals, the tentacular 

 axis with the transverse. Later writers continued the discussion. 



Korotneff's genus Cienoplana, which I obtained for the second 

 time in New Guinea waters (" On Ctenoplana" Quart. Journ. 

 Micro. Sci. vol. xxxix. 1896), seemed to me at that time to be 

 capable of throwing light on this question. Professor Arnold 

 Lang, of Ziirich, had compared the Ctenophore with the Polyclade 

 organization, and I, for one, was penetrated with the conviction 

 that biradial symmetry must have preceded bilateral symmetiy. 

 It is now clear that there is no such consecutive necessity ; and 

 it appears that the dorsiventrality of Ctenojjlana, approximating 

 it to the facies of a flatworm, is a very interesting piece of 

 convergence. 



The question has been re-opened quite recently by Th. 

 Mortensen (" Otenophora." Danish Ingolf-Exped., Copenhagen, 

 1912), apropos of the new sessile Ctenophore, Tjalfiella tristo7na 

 Mrtsn. 



Incidentally Mortensen throws doubt upon the accuracy of my 

 figures of sections showing the peculiar genital ducts of Ctenoplana 

 korotneffi ; but in so doing he is hardly justified *. I may say, 

 however, that if the morphological comparison between the 

 secondary axes of Radiata {s. sir.) and the principal axes of 

 Bilateralia were not fallacious, then the relations exhibited by 

 Bolina would point to the opposite identification to that which I 

 advocated on the basis of Ctenojdana (tentacles in the sagittal 

 plane), but to that which Agassiz advanced on tlie basis of 

 Phurohrachia (tentacles in the transverse plane). 



R. Woltereck (" Wurmkopf, Wurmrumpf, und Trochophora," 



* In Ctenoplana Tcorotneffi there were four testes onlj-, in two pairs, paired 

 about the tentacle axis. In one individual there were twelve ducts distributed 

 equally among the four testes. Of these ducts I observed the actual opening to the 

 exterior in six instances, in section. In another individual seven ducts altogether 

 were counted in a series of sections. 



With regard to the systematic position of Ctenoplana, Abbott says " it must be 

 conceded that Ctenoplana stands midway between Cceloplana and the Cydippid 

 Ctenophores, in regard to its prim itiveness or its degeneracy." And again": "The 

 weight of the morphological evidence bears out the conclusion that Cceloplana is a 

 very highly specialized Ctenophore derived from the Cydippida." (James Francis 

 Abbott; "The Morphology of Cceloplana," Zool. Jahrb., Anat. xxiv. 1907, pp. 41- 

 70, pis. viii.-x, and 7 text-figures.) 



