TV 



PHYLUM CCELENTERATA 



219 



phora is distinguished by having a rounded body somewhat produced 

 at the oral pole, and by the aperture of the tentacle-sheath being 

 on a higher level than the funnel. In the species plumosa the 

 stomodaeal 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 Crolenterates, the Hydrozoa and 

 Actinozoa, the organisation of the Ctenophora, if we leave out of account the 

 Platyctenea, is remarkably uniform. This is due to the fact that nearly all 



l.Callianira 



2.Euchlora 



3. L arrive Ha 

 FIG. 169. Three Cydippida. ab. p. aboral process ; mth. mouth. (After Chun.) 



the species are pelagic, none are colonial, and none form skeletons. Never- 

 theless a very great diversity of form is produced in virtue of differences in 

 proportiors and of 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 body in 

 the lateral plane in some genera, e.g. Euchlora (Fig. 169, 2), the result being an 

 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 

 Cattianira (/), 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. 



