8 DEFINITION OF TERMS. 



surface a secondary investment of very various constitution in the different groups ; and we 

 may, moreover, conceive of the entire animal with its digestive tube, tentacula, gangUon, 

 muscles, generative organs, circumambient fluid, and investing sacs, repeating itself by 

 gemmation, and thus producing one or more precisely similar systems holding a definite 

 position relatively to one another, while all continue organically united, and we 

 shall then have the actual condition presented by the Polyzoa in their fully developed 

 state. 



Definition of Terms. 



The old notion, which, by mistaking the zoological rank of the Polyzoa, erroneously 

 referred them to the class of the Polypes, caused the same terms to be applied to them which 

 were also used to designate the various parts of the true Polypes. The recognition, however, 

 of a type of structiu'e in the Polyzoa totally distinct from that of the Polypes proper, 

 necessitates a change in the terminology employed in their description. On these grounds 

 I have ventured to substitute some new terms for those previously used, while our increased 

 knowledge of polyzoal structure necessitates the use of certain additional terms of which we have 

 no representatives in the descriptive terminology of previous authors. For the term Polype, 

 therefore, originally applied not only to the polypoid Radiata, to which its use ought to be 

 confined, but also to the retractile portion of the Polyzoa, I have substituted in the following 

 memoir that of Polypide.* To the common dermal system of a colony, which, as well as the 

 solid basis of the true polypes, was formerly known under the names of Polypary and 

 Polypidome, I have applied the term Ccencecium.-f The ccencEcium is composed almost 

 universally of two perfectly distinct tunics ; to the external I have given the name of Ectoci/st,\ 

 and to the internal that of Endocyst.^ The sort of disc or stage which surrounds the mouth 

 and bears the tentacula, I have called Lophoj)hore.\\ The Ep'stome% is a peculiar 

 valve-like organ which arches over the mouth in most of the fresh-water genera. The 

 Perigastric** space is the space included between the walls of the endocyst and the alimentary 

 canal. 



Tlie terms now enumerated are such as I believe the nature of the subject strictly 

 requires. I employed most of them in my 'Report on Fresh-water Polyzoa' published in 

 1850, and though I am fully aware that the changing of an established terminology is 

 highly objectionable where it can possibly be avoided, yet in the present case, where new 

 facts have been accumulated requiring new words for their expression, and where the very 

 same terms have been in two different classes of animals loosely applied to organs in no 

 respect homologous, the purposes of a rigidly scientific description can, I believe, only be 

 served by some such change as that suggested. 



Besides these terms, and some which will be explained as they occur, two others in 

 common use ought to be here defined. The cells are the little chambers of which the 

 ccenoccium is made up, and in each of which a polypide is lodged. The part of the cell 

 through which the polypide admits of protrusion and retraction is the orijice of the 

 cell. 



*rioAii7roi!c, jTcoc- t Koii'oc, o'lKiov. X Ektoc, Kvariq. § Ei'COi', Kvaric. \\ Ao^oc, <popii»>. 

 ^ Etti, aroiia. ** Ofoi, yaanio. 



