DIVISIOXS OF THE HYDEOZOA. 



61 



Order II. Gorynida. 



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

 Corynida or Tuhularida, we have a number of organisms which 

 in their essential structure are closely relate<.l 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 moie than a 

 single poly]iite. In these cases there is an exceedingly close ap- 

 proach to the structure of the com- 

 mon Hydra, but the jjolypite is 

 permanently fixed without the 

 power of voluntarily changing its 

 place, whilst the I'eproductive pro- 

 cess is considerably diff'erent. 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 coenosarc, and 

 all forming parts of a plant-like 

 rooted colony. In scjnie of the 

 Corynida the polypites are naked, 

 but in most cases the crenosarc is 

 protected by a horny-locjking chit- 

 inous ^ envelope or " polypary," as 

 in I'uhularia indivisa (fig. 31). In 

 no case, however, is this horny 

 covering so prolonged as to form 

 little cups in which each jiolypite is 

 contained. It always stops short 

 at the bases of the polypites, and in 

 this way the Corynida can always 

 be distinguished from their near 

 allies, the Sea-firs {Sertularida). 



Good examples of the Corynida 

 are the common Pipe - corallines 



(Tiibidaria), in which the cwnosarc is enclosed in a homy tubular 

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



' Chitine is a suTistance wliicli is nearly allieil to horn, luit is distinguished 

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



. 31.— Fragment of Tvlndaria 

 indirim, natural size. 



