222 



ZOOLOGY 



SECT. 



sheath being on a higher level than the funnel. In the species 

 plumosa the stomodreal ridges are of a brown colour, and the leaf- 

 like branchlets of the tentacles yellow. 



3. GENERAL ORGANISATION. 



Compared with the two former classes of Ccelenterates, the Hydrozoa and 

 Actinozoa, the organisation of the Ctenophora is remarkably uniform. This is 

 due to the fact that all the species are pelagic, none are colonial, and none form 

 skeletons. Nevertheless a very great diversity of form is produced in virtue of 

 differences in proportion and modifications of the tentacular and canal systems. 



The Cydippida agree in all essential respects with Hormiphora, the most 

 important deviation from the type-form being the compression of the bocty in the 

 transverse plane in some genera, e.g. Euchlora (Fig. 168, 2], the result being an 



mlti 

 l.Callianira 



2.Euchlora 



S.LampeMa 



FIG. 168. Three Cydippida. ab. p. aboral process ; mth. mouth. (After Chun.) 



oval instead of a circular transverse section, with the tentacles at the end of the 

 long axis. The aboral pole may be produced into wing-like appendages, as in 

 CaUianira (1), and in Lampetia (3) the mouth is so dilatable as to form, when 

 expanded, a sole-like plate by which the animal retains itself on the surface of the 

 water or creeps over submarine objects. In EnchJora rubra minute nematocysts 

 have been found, and there is reason to believe that it was by the modification 



