DIVISIONS OF THE HYUKOZOA. 



61 



Order II. Corynida. 



In the second order of the Hydroid Zoophytes, known as "the 

 Corynida or Tubularida, we have a number of organisms which 

 in their essential structure are closely related to the Hydra, but 

 which differ considerably in the nature of the reproductive pro- 

 cess. All of them are marine, with the single exception of the 

 genus Cordylophora, which inhabits fresh water. Some of the 

 members of the order are simple, consisting of no more than a 

 single polypite. In these cases there is an exceedingly close ap- 

 proach to the structure of the com- 

 mon Hydra, but the polypite is 

 permanently fixed without the 

 power of voluntarily changing its 

 place, whilst the reproductive pro- 

 cess is considerably different. In 

 the majority of the Corynida, how- 

 ever, the hydrosoma is compound, 

 consisting of a greater or less num- 

 ber of separate polypites or zooids, 

 all connected with one another by 

 a common flesh or coenosat*c, and 

 all forming parts of a plant-like 

 rooted colony. In some of the 

 Corynida the polypites are naked, 

 but in most cases the coenosarc is 

 protected by a homy-looking chit- 

 inous 1 envelope or " polypary," as 

 in Tuhularia indivisa (fig. 31). In 

 no case, however, is this horny 

 covering so prolonged as to form 

 little cups in which each polypite is 

 contained. It always stops short 

 at the bases of the polypites, and in 

 Ithis way the Corynida can always 

 /pe distinguished from their near 

 allies, the Sea-firs {Sertularidd). 



Good examples of the Corynida 

 are the common Pipe - corallines - 



(Tiihularia), in which the coenosarc is enclosed in a homy tubular 

 polypary (hg. 31), each tube containing a single polypite. Other 



^ Chitine is a substance which is nearly allied to horn, but is distinguished 

 from it by the fact that it is not soluble in caustic potash. 



Fig. SI.— Fragment of Tuiularia 

 indivisa, natiu-al size. 



