11 INTRODUCTION. 



to burthen technical language with a multitude of harsh- 

 sounding Greek compounds is to check, and not to aid, the 

 cultivation of science. The aim should be to combine 

 definiteness with simplicity, as far as possible. 



The following List includes the principal terms with 

 which the student of the Hydroida should be familiar : 



ZOOID. Any one of the principal elements, more or less 

 independent, that make up the complex individuality of 

 the zoophyte, e.g. the polypite, the reproductive body, 

 whether fixed or free, &c. 



POLYPITE. The alimentary or nutritive element of the 

 Hydroid colony, consisting of a digestive sac, with a ter- 

 minal opening (mouth) and organs of prehension (ten- 

 tacles). Occasionally the adult zoophyte consists of a 

 single polypite, as in Myriothela, Corymorpha, and Hydra ; 

 but generally a large number, the product of successive 

 buddings, are organically united, so as to form a compo- 

 site and plant-like structure. 



. The common flesh or trunk, which unites 

 and binds together the polypites in a compound zoophyte. 

 The following parts must be distinguished in it : the stem, 

 which is sometimes simple and sometimes branched, and the 

 adherent base* or stolon, which roots the zoophyte to the 

 surface on which it grows. The latter is generally filiform 

 and reticulated ; but in some cases it occurs as a solid, 

 chitinous crust (Hy dr actinia) . 



POLYPARY. The chitinous f sheath or tube which encloses 



* The former of these is the hydrocaulus of sortie writers, and the latter 

 the hydrorhiza. 



t Chitine is a suhstance resembling horn, but differing from it in chemical 

 composition. 



