Sl'RL'CrURE AND DEVELOPMENT OF a)EL(Jl'L.\NA. 67 



very highly specialized ctenophore, derived from the cydippida" (p. 62). 

 But, I can not agree with his argument upon the homology of the 

 canal-systems of Cocloplaiia and cydippid. He started that argument 

 from a conception that the flatness of the body of Cocloplaiia had been 

 derived merely from the reduction of the principal axis of the cydippid. 

 It was accordingly but natural for him to have arrived at some 

 conclusions, evidently erroneous, as for instance that, "The Cydippid 

 mcrich'onal canals have disappeared in Cocloplaiia''. (p. 65). 



As already mentioned, Mortensen seems to be in an opinion, on 

 the homology of the creeping surface of platyctenids, somewhat different 

 from KoRSCHELT & Heider, Hatschek, and others. He has given, in the 

 description of the development of Tjalfiella, that, a peculiar " transverse 

 furrow " appears on the ventral side of the body of the cydippid-hke larva, 

 which furrow divides the ventral part of the larva into a pair of lobes 

 and by the out-folding of the lobes the flat sole of the adult is formed. 

 The alleged transverse furrow, however, seems to be nothing else than 

 the oral aperture of the larva which has become elongated in the 

 transverse direction. This fact will be readily seen, if one examines the 

 origin and fate of that furrow in Mortensen's descriptions and compares 

 that with the same of the oral aperture of Cocloplaiia given in the 

 forgoing pages. Further, the fact that, the inner surface of the furrow 

 is lined with an epithelium of the same character as that of the upper 

 part of the pharynx, affords another evidence of that furrow being 

 nothing but the oral aperture. 



Krempf ('20, c, '21) also regards the ventral aperture of the larva 

 of Cocloplaiia not to be the mouth, nor the cavity which the aperture 

 leads into to represent the pharynx. This argument he has based 

 mainly upon the fact that the aperture and cavity are much wider in 

 the transverse direction than in the sagittal. But such condition of the 

 aperture and cavity obtains only in the relatively advanced stage of 

 development, both of them being almost equally wide in every direction 

 in the earlier stages; consequently it is futile to lay much stress upon 

 such. a condition of the aperture and cavity. The development of the 

 animal described above shows plainly that the parts mentioned arc 

 to be identified with the mouth-aperture and pharynx of ordinary 

 ctenophores. Further evidence for my opinion on the homology of the 

 ventral surface is given already. 



It may then be taken as granted that, Coeloplana is a highly 

 specialized ctenophore adapted to creeping life instead of floating, and 



(luI LI B R AR V ^ 



