212 



ZOOLOGY 



APPENDIX TO CTEXOPHORA 



CTEXOPLAXA AND OELOPLANA. 



Before leaving the Ctenopkora mention must be made of two remarkable 

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

 Turbellaria Polj-cladida, or Planarians, a group of worms to be described in 

 the following section. 



(.'t< noplana (Fig. 159) is a small marine animal, nearly circular in outline, 

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

 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 

 an otolith surrounded by eight radiating ridges (r.r.), alternating with which 

 are as many clefts ('/.), each containing a protrusible row of stiff processes, 







2 



\gBix ; ' . f- 



, 





' ' :''"''" 



Fu.. l.v.>. Ctenoplana kowalevskii, A. hvm above, II. fi-ma the side. ct. clefts; r. r. 

 radiating ridges ; *. <i. seiisu-ury.iii. lAt'tei- K'ii-"tiieft'.) 



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 formed 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. 



< 'ulu/Jiiua is found in the Pved Sea. It is also flattened dorso-ventrally, 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-organs, 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. 



