CTENOPHORA. 



31 



24. 1907) ') several important additions have been made to our knowledge of this highly interesting 

 Ctenophore. 



There is no folding plane, the animal having acquired a quite Planarian-like habit. The gastro- 

 vascular system affords some essential points of resemblance to Tjalfiella. The stomodseum contains 

 in its outer part (the pharynx) a rich system of folds, the inner part (the oesophagus) being narrow 

 and provided with long cilia as in Tjalfiella and Ctenoplana. From the infundibulum two uubranched 

 tubes rise towards the dorsal side, both unbranched and both opening to the exterior; "as in the 

 typical Ctenophores these arise in such a position that along the tentacular plane the lower one is to 

 the right, the upper one to the left of that plane". In Tjalfiella (the grown animal) only one of the 

 tubes has been definitely shown to open to the exterior, the opening lying nearly in the sagittal 

 plane. In Ctenoplana no opening has been found. In any case they all agree in the tubes being 

 simple, and I suppose future researches will show them to agree also as regards the opening of the 

 tubes and the position of these openings. 



As in Tjalfiella and Ctenoplana there is a branching peripheral canal system arising from the 

 main branches of the gastrovascular system. As in Ctenoplana a pair of sagittal lobes proceed from 

 the infundibulum, and these lobes give rise both to the peculiar dorsal respiratory tubes and to branch- 

 ing canals which anastomose with the other peripheral canals. The histological structure of the 

 canals appears to be as in Tjalfiella, judging from Taf. 9, Fig. 14, of Abbott's memoir. — There thus 

 seems to be accordance in the main points regarding the structure of the gastrovascular system in 

 all the three genera, the non-existence of the sagittal lobes in Tjalfiella being probably an adaptation to 

 its body shape, and thus of secondary importance; likewise the fact that the peripheral canals are 

 anastomosing in Ctenoplana and Coeloplana, not anastomosing in Tjalfiella seems to me of minor 

 importance. — (Regarding the origin of the sagittal lobes as explained by Abbott for Coeloplana 

 (Op. cit. p. 64—65) I confess that I feel rather convinced of the incorrectness of this explanation, in 

 which the pharyngeal vessels, not existing in Tjalfiella, play an important role; but to enter on this 

 point here I find of little use, especially so long as the development of Coeloplana is completely 

 unknown). Regarding the genital organs, which have not yet been observed, it may not be unreasonable 

 to expect that they will prove to agree in the main points with those of the two other genera, and 

 that their relation to the gastrovascular system in both Coeloplana and Ctenoplana will prove to be 

 essentially as in Tjalfiella. 



') Abbott's "Preliminary Notes on Coeloplana", in Annot. Zoolog. Japonenses. IV. 1902. p. 103 — 108, contain some 

 information not included in his final paper. Thus e. g. the following highly interesting statement (p. 105): "It not only crawls 

 in any direction whatever but it frequently goes in more than one direction at once and the two halves, starting off for 

 opposite sides..., often stretch the middle part to the breaking point". - Further the statement "where one is found, others 

 are quite sure to be, and the situations in which thej- are found are sometimes strongly suggestive of multiplication by divi- 

 sion, tho no evidence has been obtained yet as to that point" is worth recollecting in connection with the above remarks on 

 the regeneration of Tjalfiella. 



Concerning the tentacles it is stated that "the secondary- branches are covered with batteries of nettle cells". In 

 the final paper (p. 56) these branches are stated to be "covered with typical Ctenophoral adhesive cells (lassocells, coUoblasts) 

 that sometimes, when the tentacle is fully extended, appear to be arranged in groups or batteries" — no mention being made 

 of the "nettle cells", which are evidently due only to a less precise terminology. This fact has, unfortunately, occasioned 

 a separate generic name for the Japanese Coeloplanas. Schouteden in his paper "Les affinites des Ctenophores et Polyclades" 

 (Ann. soc. Zool. et Malacol. de Belgique. XI. p. 1905. CXVII), establishes for these forms, mainly on the supposed presence 

 of nematocysts, otherwise unknown among Ctenophores (the often quoted exception, Eiichlora rubra, according to Samassa, 

 Op. cit. p. 173, has not nematocysts) a separate genus, Psetuiococloplana. This name, evidently, must be dropped -again as a 

 synonym only of Coeloplana. 



