CLASSIFICATION OF RADIATA. 453 



proposes the name of CCELENTERATA ; it includes the following 

 Classes : 



II. POLYPIFERA, or Polypes. This Class includes the highly 

 organised Polypes already alluded to ( 1084), in which the 

 stomach is furnished with a proper membrane, separated by a 

 certain space from the integument of the animal. They are 

 either simple or compound, and usually fixed by their base to 

 submarine objects, or imbedded in a horny, fleshy, or calcareous 

 polypidom. 



III. HYDROZOA. In this Class, which includes a great variety 

 of forms, the intimate connection of which has only been clearly 

 shown by the researches of modern Naturalists, the animals, as 

 in the preceding group, are either simple or compound. They 

 are all of a gelatinous texture, and furnished with a digestive 

 cavity, which is merely hollowed out in the substance of the 

 body ; but in other respects they exhibit a great diversity both 

 of external form and internal structure. The fundamental form 

 is that of a Polype (Hydroid Polypes), a few being simple, but 

 the majority compound ; but of these a considerable number 

 give origin by gemmation to independent, free-swimming crea- 

 tures of far higher organisation, possessing a vascular and repro- 

 ductive system, besides organs which must be regarded as con- 

 nected with the senses (the Pulmograde Acalephce or Discophora 

 of authors) ; whilst some species appear to be floating colonies of 

 Hydroid Polypes, and others are free-swimming simple animals, 

 which move by the aid of cilia. The latter, in the editor's 

 opinion, would be better placed in a Class by themselves ; but 

 they will be retained here amongst the Hydrozoa, in accord- 

 ance with the general custom. 



