INTERRELATIONSHIP OF THE MEMB1':RS Ol' I'LATVCTENEA. 



91 



ordinaiy pinnate tentacles, in the remaining orders the tentaces may be 

 entirely lacking (Beroidea), or replaced by the peculiarly modified 

 " secondary " tentacles (Lobatea & Cestidea). Finally, the out-spreading 

 of the pharynx is nicely foreshadowed by a cydippid, Lampetia, as it has 

 been pointed out by previous writers. With the Lobatea, the Platyctenea 

 is evidently more remotely related than it might appear at first sight, 

 since it differs rather strikingly from that order in the relative length 

 of the sagittal and transverse axes of tlie body, in the conditions of the 

 tentacular apparatus, of the canal system, but especially of the pharynx. 

 The " lobes " characteristic of the Lobatea should be looked upon as 

 the outgrowth from the oral parts of the body and can not be 

 homologized with the parts that have given rise to the body-skirt 

 characteristic of the Platyctenea. While in the formation of the lobes 

 the pharynx is not concerned at all, the skirt of the Platyctenea develops 

 b\' the out-opening of the pharynx; the former arise form the parts 

 below the level of the oral aperture but the latter from the parts above 

 it. 



Then, the diagram of illustrating the mutual relationship of all 

 the orders of the Ctenophora as well as the origin of the Turbellaria 

 mav be somewhat as shown below : 



Turbellaria Platyctenea Lobatea Cestidea Beroidea 



Cydippidea 



