ACTINOZOA. 









229 



on 



each side of the mouth. Of these, 



one is 



simple, while the others display a number or 

 lateral ramifications. But all these structures 

 require to be investigated anew. 



In habit the Ctenophora resemble the oceanic 

 Hydrozoa, like them swimming near the surface 

 in calm weather, and again descending on the 

 approach of showers. Like them, also, their deli- 

 cate structures rapidly disappear when removed 

 from the sea-water and exposed to the rays of the 

 sun, an almost imperceptible film remaining the 

 only trace of what was erewhile an active and 

 beautiful organism. Yet are the Ctenophora very 

 voracious, feeding on a number of floating marine 

 animals, among which their own kindred seem 

 especially to be preferred. The prey, once swal- 

 lowed, is assimilated with a rapidity which to 

 some may seem strange, when the simple structure 

 of the digestive apparatus is considered. All the 

 Ctenophora are not equally fragile. Pleuro- 

 bvachia, in spite of its tender gelatinous aspect, 

 may be preserved in captivity for weeks, or even 

 months, if properly supplied with food. 



The Ctenophora swim in various positions, and 

 some may often be noticed with their apical ex- 

 tremity turned downwards or forwards. Hence 

 many writers term this the dorsal aspect; the 

 digestive sac, by a strange perversion of language, 

 being described as situate below the funnel ; and 

 so with the relative positions of the remaining 

 organs. This practice is not only objectionable in 

 itself, but has tended much to confuse almost 

 every published account of the structure of a 

 group of beings, than which few anatomical sub- 

 jects are at once so easy and so accessible. Not 



Q 3 



