44 CTENOPHORA. 



Coelomata are thought to have originated from the Cerianthidse, the result thus being the diphyletic 

 origin of Bilateralia, as expressed in the following diagram. 



Archiplanoidea- 

 Cerianthidse - 



' Ctenophora 

 -Plathelminthes 

 Anthozoa 

 , Coelomata 



Mainly in accordance with the views of Willey (though without knowing — at least without 

 quoting — his paper on Ctenoplana) E. v. Bene den') expresses the opinion that the Ctenophora are 

 'des Planariens adaptees a la vie pelagique". He does not otherwise enter on a discussion of this 

 problem. — Likewise Dawydoff in his description of Hydroctena Salenskii^) does not enter on a dis- 

 cussion of the relations between Planarians and Ctenophores, stating only that they are "indubitables", 

 resting on fundamental embryological characters; but he gives the following graphic representation of 

 the Ctenophoran affinites: 



,, J ,j ^,^' Hydroctena Ctenophores 



Hydromeduses ^^^ ^ 



(probablement Narcomeduses) ^---^-. Ctenoplana Coeloplana Turbellaires 



In 1902 James Fr. Abbott gave a preliminary note 3) on Coeloplana, but it was not before 

 1907 that the full report was published 4), in which we get at length some very much wanted infor- 

 mation about the morphology of this highly important form. Unfortunately the specimens found by 

 Abbott (at Japan) were altogether immature, so that the morphology of the genital organs and the 

 development still remain unknown. The main result of Abbott's researches is that Coelopla>ia can 

 by no means be regarded as a primitive form (— and according to Willey it should be the most 

 primitive of all — ). "The weight of morphological evidence bears out the conclusion that Coeloplana 

 is a very highly specialized Ctenophore, derived from the Cydippida". (Op. cit. p. 62). As "vestigial 

 structures reminiscent of a previous pelagic habit" are especiall}- pointed out: the otolith and the 

 rosettes (the latter being apparently superfluous structures on account of the ramifying gastrovascular 

 canals and of the very small amount of parenchyma, the nutritious fluid being thus directly trans- 

 ported to all parts of the body, while in typical Ctenophores the rosettes are thought to serve as 

 carriers of the nutritious fluid into the thick layer of parenchyma). In view of the assertion of Lang, 

 quoted above (p. 41), that it is "ein unabweisbares physiologisches Postulat . . . dass bei Coeloplana die 

 Anpassung an die kriechende Lebensweise eine grosse Veranderung in der Anordnung der Muskulatur 

 und damit des motorischen Nervensystems nach sich gezogen habe", it is interesting to note that 

 Abbott states the muscular system to be much more developed than in typical Ctenophores; unfor- 

 tunately he does not give a more detailed description of the musculature, so that it cannot be seen in 

 which features it differs from that of other Ctenophores. The fact that a basement membrane is 

 developed as a sort of skeletal support for the muscles as in the Polyclads — and as is also found in 



1) Les Anthozoaires de la "Plankton-Expedition". Ergebn. d. Plankton-Exped. d. Humboldt-Stiftung. II. K. e. 1898. p. 182. 



2) Mem. Acad. imp. St. Petersbourg. 8. Ser, 14. 1904. 



3) James Francis Abbott. Preliminary Notes on Coeloplana. Annot. Zoolog. Japonenses. IV. p. 103—108. 



4) James Francis Abbott. The Morphology of Coeloplana. Zool. Jahrb. .\bt. f. Anat. Bd. 24. 1907. p. 41 — 70. Taf.8— lo- 



