126 INVERTEBRATE MORPHOLOGY. 



from the Coelentera and associated with the Turbellaria, being regarded 

 as highly modified forms, adapted for pelagic life, descended from Tur- 

 bellarian ancestors. The evidence which has been brought forward in 

 favor of a relationship of the Turbellaria to the Coelentera through the 

 Ctenophores would support this view as well as that it was intended to 

 support, and to this may be added the fact that while the peculiar adhesive 

 cells of the Ctenophores cannot be homologized with any of the histological 

 elements of the Cnidaria, they may readily have been evolved from the 

 adhesive cells which occur in the ectoderm of many Turbellarians. 



SUBKINGDOM METAZOA. 



Class Ctenophora. — Pelagic organisms provided with eight meridional rows 

 of plates formed by the fusion of cilia. 



1. Order rewtocwZato.— Ctenophora provided with tentacles. 



(a) Without lobes ; more or less oval in shape. Pleurobrachia, 



Mertensia. 

 (6) Lateral lobes occurring at oral pole. BoUna, Mnemiopsis. 

 (c) Ribbon-like form. Cestum. 



2. Order EtirystomecB.—^M'houi tentacles ; stomodseum wide and 



bell-like. Beroe, Idyia. 



LITERATURE. 



R. Hertwig. Ueber denBau der Gtenophoren. Jenaische Zeitschr., xiv. 1880. 

 C. Cliiin. Bie Gtenophoren des Golfes ton Neapel. Fauna und Flora des Golfes 

 von Neapel. Monogr. i. 1880. 



