584 



TAKU KOMM. 



out in an almost film-like manner (Fig. 5). Thus, the larval body may 

 now be said to represent a somewhat hump-like elevation in the central 

 parts of a broad and thin basal expansion. It is easy to imagine that 

 by gradual depression of the elevation, the entire body would assume 

 the habitus of the adult. But stages representing this change have not 

 co:ne under actual observation. 



Of individuals which have completely changed into the adult shape 

 and which were taken from the alcyonacean host, the smallest and 

 youngest observed was one only about I mm. in diamètre. The most 

 notable points in this little specimen were the facts that the gastrovas- 

 cular system consisted of eight broad and subequal pouches arranged 

 radially around a central cavity representing the infundibulum, and that 

 there exists the peripheral canal-system consisting as yet of a sparse 

 number of anastomosing canals. Of the eight radial pouches, the four 

 in relation with the base of tentacles evidently represent the tentacular 

 canals, and the remaining four the meridional canals, of the adult. 



Conclusion. — In the light of the developmental facts noted above 

 in brief, it goes beyond the reach of doubt that Coeloplana represents 

 a highly specialized form of the Ctenophora. In fact, it will be conceded 

 to by all that the genus appears to have been derived from a cydippid 

 ancestral fo:m by a loss of certain old characters and by concomitant 

 acquirement of a series of new ones in adaptation to the change in 

 habit of life from the pelagic to the creeping. Most remarkable is the 

 undeniable indication that the entire creeping surface (ventral body 

 surface) of Coeloplana was derived by the turning out of a large part 

 of the inner pharyngeal surface of ordinary cydippids. It then seems 

 that the flatness of body in this aberrant form of ctenophores may be 

 regarded to be in a large measure due to that fact, and is not to be 

 explained by assuming merely the reduction of vertical body-axis, as 

 was done by Lang* and several other authors. 



* Lang, A. (1884). Die Polycladen des Golfes von Neapel. Fauna u. Fbra d. Golf. 

 Neapel. Monogr. XI. 



