86 T, KOMAT : STUDIES ON TWO ABERRANT CTENOPHORES 



assigned to ? To answer this, it is evidently necessary to ellucidate the 

 change undergone by the animal after the liberation from the body of 

 the host. Nevertheless, the observation on the parasitic stage decides 

 that, the animal bears close relationship to the Platyctenea on one 

 hand and to the Cydippida on the other. Above all, the fact that the 

 ventral surface of the body is lined all over with the ciliated epithelium, 

 as also that profuse foldings are developed in the central parts of that 

 surface, shows clearly that the ventral surface of Gastrodes is morpho- 

 logically homologous with that of platyctenids. Then, the surface may 

 be regarded to have arisen by the out-turning of the pharynx, and this 

 is the feature that characterizes most the group Platyctenea. Besides, 

 the flatness and dorsi ventral ity of the body of the animal, as well as 

 the arrangement of the parts of the body, especially that of the canal- 

 system, can be accounted for only by assuming such a change as 

 mentioned above having affected the body of Gastrodes. 



Clear as the af^nity of Gastrodes to the Platyctenea in these 

 respects, it can not be denied that in other respects the resemblance is 

 rather slight. The animal has no bright coloration, nor any branching 

 canal system, and it is provided with pharyngeal canals which lack all 

 platyctenids thus far known. Furthermore, it shows a great deviation from 

 those forms in the condition of the gonad. I5ut, it should be mentioned 

 as well that, the habitat of Gastrodes in the body of Salpa apparently 

 makes it necessary for the parasite to retain the original colourless and 

 transparent condition. The difference in the condition of gonads differen- 

 tiates the form from all the members of the other orders of the Ctenopho- 

 ra as widely as from those of the Platyctenida. Towards the Cydippida, 

 the form approaches especially in the conditions of the canal-system — 

 for instance, the meridinal canals are simple and the pharyngeal canals are 

 developed. In short, so far as can be judged from the condition of the 

 parasitic stage, Gastrodes shows undeniable relationship to the Platyctenea 

 on one hand and to the Cydippida on the other. But, the fact that 

 the form shares with the former order the most characteristic feature of 

 the structure of the body, viz. the out-spreading of the pharynx into 

 the ventral body surface, apparently makes the form to be grouped into 

 the order Platyctenea. 



The presence of a planula stage in this form, however, is unique 

 in the entire group of the Ctenophora,* and may be said to differentiate 



* Chun ('8o) has given that lie olisersed very delicate cilia covering the surface of the 

 l)()(ly of a certain larval stage of Iittcharis; perhaps, this stage represents the planula stage. 



