22 



THE CTENOPHORA 



ORDER 4. Platyctenea. 



Ctenophora of creeping habit ; the body flattened in the principal axis 

 so that a dorsal can be distinguished from a ventral surface. No meridional 

 sub-costal canals, but a system of anastomosing peripheral vessels. Costae, 

 when present, retractile within ectodermal pouches. Genera Ctenoplana, 

 Korotneff, costae present ; Coeloplana, Kowalevsky, costae absent ; the 

 whole surface ciliated. 



S.O 



sl.c. 



ov. 



FIG. X. 



Beroe Forskalii, Chun, from the sagittal aspect, m, mouth ; i, infundibulum ; so, sense 

 organ ; pf, papilliform processes of the polar fields ; stc, stomodaeal canal ; me, meridional 

 canals ; ov, ovaries ; sp, spermaries. The peripheral canal system is seen extending over the 

 entire surface. 



SUB-CLASS 2. NUDA. Tentacles absent. 



ORDER Beroidea, Lesson. 



FAMILY BEROIDAE. Elongate, conical, or ovoid Ctenophora com- 

 pressed in the infundibular plane, with wide mouth and spacious stomo- 

 daeum. The otolith mass is uncovered, the polar fields surrounded by 



