66 T. KOMAI: STUDIES OX TWO AlilCRRANT CTENOPHORES 



dorsivoUrality of its body has been produced by the out- spreading of the 

 lower part of the pharynx. In shoit, all the evidence supports the 

 opinions of the authors ranked in (2) given in p. ()t^. As the basis of 

 this assertion, I may bring forward the statement first that, the 

 general structure of the body, showing clear biradial symmetry with 

 the sense-organ and the mouth-aperture occupying the central position 

 and the tentacular apparatus situated on each side of it, is perfectly in 

 accordance with that of all ctenophores. Further, both the aboral sense- 

 organ and the tentacular apparatus are almost perfectly identical with 

 those of cydippid ctenophores. Even the arrangement of the gastro- 

 vascular system and of the genital system, which appears at first sight 

 highly characteristic of the present form, reveals itself on closer examina- 

 tion to be a mere deviation of rather minor importance from the 

 condition prevailing in ordinary ctenophores. To mention more minute 

 histological features, the ectoderm and endoderm are practically of the 

 same structure as those of ordinary ctenophores, especially the existence 

 of colloblasts and ciliated rosettes, both in the typical forms, as well 

 as the branching of muscle-fibres at the ends, serves as a strong argument 

 in favour of Coeloplands being a genuine ctenophore. But the facts 

 regarding development are still more convincing. As shown above, 

 Coeloplana begins its development from an c<g^ of the same structure as 

 that of ordinary ctenophores and, after passing through the segmentation 

 and gastrulation stages, both showing no deviation whatever from those 

 in ordinary forms, develops into a typical cydippid larva; subsequently, the 

 stomodaeum of the larva is sectioned into an internal and an external 

 half, of which the latter is spread out into a broad and flat ventral 

 sole, while the former becomes the pharynx of the adult. The fact that, 

 the ventral surface of Coeloplana has been developeb in this way can as 

 well be seen from some anatomical features that the animal shows. As 

 already mentioned, the tentacular apparatus of this animal agrees in all 

 structural features with that of cydippid ctenophores, but it is characterized 

 b\' its horizontal disposition, and this fact may be accounted for only by 

 assuming the occurrence of such a change as mentioned just above. 

 Similar argument may be made as to the situation and arrangement of 

 the gastro-vascular system. Further, the ventral epidermis j)resents a 

 character very different from the dorsal, bu|^ much in conformity with 

 the pharyngeal epithelium. 



Aiii'.OTT ('07) has asserted, with full justice that: — "The weight 

 (jf morphological evidence bears out the conclusion that Coeloplana is a 



