222 



ZOOLOGY 



SECT. 



retractile tentacles. The canal-system is devoid of meridional canals, but 

 comprises a set of branching and anastomosing peripheral canals. The male 

 gonads only have been found : they are situated in diverticula of the canal 

 system and have been described as having independent ducts opening on the 

 exterior. 



Cosloplana has been found in the Red Sea and on the coast of Japan. It 

 is also flattened dorso-ventrally, and further resembles Ctenoplana in its 

 ventral mouth, dorsal polar sense-organ with ganglia, paired retractile ten- 

 tacles, and anastomosing canals. There are, however, no swimming-plates, 

 and progression is effected only by creeping. 



Nothing is known of the development of either of these two genera. 



Tjalfiella (Fig. 174) was found in dredgings from a depth of 500 metres 

 oft' West Greenland. Instead of being free and pelagic like the Ctenophora 

 in general, or able to creep about like Coeloplana and Ctenoplana, Tjaljiella 



FIG. 174. Tjalfiella. Adult specimen with many embryos, side view ; oral (attached) 

 surface upwards, br. c. branching canals ; e., g., i. embryos ; t. tentacle ; t. b. tentacle- 

 base. (After Mortensen.) 



is sessile in the adult condition, living attached to the stalk or polypes of an 

 Umbellula (Pennatulacea, p. 194). The body is elongated in the transverse 

 plane : shortened in the direction of the primary axis. The attachment is 

 effected by the oral surface by the agency of the inner surfaces of a pair of 

 chimney-like hollow processes, each with a wide distal opening and a ciliated 

 cavity. From the distal opening of each of these processes the corresponding 

 retractile tentacle (t.) is capable of being protruded. The slit-like mouth, 

 elongated, as in other Ctenophora, in the sagittal plane, opens out of a super- 

 ficial sub-oral cavity with folded walls with which the cavities of the chimney- 

 like processes are in free communication at their bases the latter acting as 

 secondary mouths. There are no meridional or stomodseal canals, and in the 

 adult no swimming-plates : the polar (apical) sense-organ is reduced. There 

 are four pairs of reproductive organs, each comprising an ovary and testis 

 arranged opposite one another as in Horiniphora and the Ctenophora in general, 



