IV 



PHYLUM OELENTERATA 



225 



APPENDIX TO CTENOPHORA 



CTENOPLANA AND CCELOPLAXA. 



Before leaving the Ctenophora mention must be made of two remarkable 

 organisms which have been supposed to connect the present class with the 

 Turbellaria Polycladida, or Planarians, a group of worms to be described in 

 the following section. 



Ctenoplana (Fig. 172) is a small marine animal, nearly circular in outline, 

 flattened dorso-ventrally, and alxmt 6 mm. in diameter. It has hitherto been 







Fin. 17-2. Ctenoplana kowalevskii. A, from above; B, from the side. cl. clefts ; r. r. 

 radiating ridges ; s. o. sense-organ. (After Korotneff.) 



found only twice once in the Indian Ocean and once in New Britain. Instead 

 of swimming freely, like a Ctenophoran, it creeps on its ventral surface, like 

 a worm. In the centre of the dorsal surface is a vesicle (s.o.) containing a mass 

 of lithites surrounded by eight radiating ridges (r.r.), alternating with which 

 are as many clefts (cl.}, each containing a protrusible row of stiff processes, 

 resembling the swimming-plates of Ctenophora. The mouth is in the centre 

 of the ventral surface, and leads into a stomach, from which are given off 

 numerous anastomosing canals, as well as a vertical canal which passes upwards 

 and ends beneath the sense-organ. In diverticula of this system are found the 

 testes, which have independent ducts opening on the exterior. There are two 

 solid tentacles contained in sacs, and a nerve-centre lies beneath the sense-organ 

 (*.o.). Beneath the ectoderm is a basement -membrane, which acts as an organ 

 of support, and the muscular system is complex. Near each tentacle is an 

 aperture leading into a branched canal which is probably excretory, like the 

 nephridial tubes of Flat-Worms. (See Section V.) 



C"-lf>ftlana is found in the Red Sea. It is also flattened dorso-veiitrally, but 

 is oval instead of circular in outline, its dimensions being about 6 by 4 mm. It 

 resembles Ctenoplana in its ventral mouth, dorsal sense-organ, paired retractile 

 tentacles, and complex system of anastomosing canals from the stomach. There 

 are, however, no swimming-plates, and the ectoderm is ciliated. 



Nothing is known of the development of either genus. 



Q 



