36 A Guide to the Zoological Collections in the 



(7) The generative products arise in diverticula of the 

 stomach, and not, as in the Hydromedusse (as 

 is so well shown in Olindias millleri), from 

 the ectoderm. 

 The Scyphomedusx are usually free-swimmers through- 

 out the whole of their existence, but in the family Lucer- 

 naridcB they are attached by their aboral pole in the adult 

 stage , 



The Scyphomedusx being exceedingly delicate animals, 

 are not easy to preserve for Museum purposes, and in this 

 collection they are represented only by the usual glass 

 models, and by spirit specimens of the deep-sea form 

 Atolla. 



4 CNIDARIA CTENOPHORA. 



[Ilorthcm txCss of Cnsf: 7]. 



In the Ctenophora the simple polyp type is much modi- 

 fied, and, as in the Scyphomedusse, the modification is such 

 as to fit the animal for a freely locomotive life at the 

 surface of the ocean. Locomotion, however, is effected 

 not so much by the contraction of muscles as by the 

 rowing action of special processes of the ectodermal 

 cells known as "cilia." The cilia are collected together 

 in rows which much resemble combs (hence the name 

 Ctenophora or "comb-bearers"), and the combs of cilia are 

 usually disposed in eight bands or meridians which pass from 

 pole to pole of the usually spherical or ovate or helmet- 

 shaped body. These rows of combs of cilia are very well 

 displayed in the spirit specimens of Beroe ovata and Cydippe 

 plumosa. The internal structure of the typical Ctenophor 

 is not essentially different from that of the Medusa : the 

 mouth leads by a much-compressed gullet into a long 

 stomach placed crosswise to the gullet, and from this 

 stomach a number of canals radiate throughout the bedy. 



The sensory organ of the Ctenophors is single and is 

 situated at the aboral pole of the body. 1 he Ctenophora 

 are very delicate animals, and are very difficult to preserve, 



