DIVISIONS OF THE HYDROZOA. 



61 



polypites or zoo'ids, all connected with one another by a com- 

 mon flesh or ccenosarc, and all forming parts of a plant-like 

 rooted colony. In some of the Corynida the polypites are 

 naked, but in most cases the ccenosarc is protected by a 

 horny-looking chitinous * envelope or " polypary," as in 

 Tubularia indivisa (Fig. 14). In no case, however, is this 

 horny covering so prolonged as to 

 form little cups in which each poly- 

 pite is contained. It always stops 

 short at the bases of the polypites, 

 and in this way the Corynida can al- 

 ways be distinguished from their near 

 allies, the sea-firs (Sertularida). 



As a good example of the Cory- 

 nida, the common pipe - coralline 

 (Tubularia indivisa) may be taken. 

 In this animal (Fig. 14) we have a 

 gregarious zoophyte consisting of 

 numerous clustered horny tubes, fixed 

 by their bases to shells or stones, and 

 inhabiting most seas. The tubes are 

 usually unbranched, though often con- 

 siderably interwoven together. Each 

 tube is filled with a soft, semi-fluid, 

 reddish ccenosarc, and gives exit at 

 its free extremity to a single poly- 

 pite. The polypites are bright red in 

 color, and are not retractile within 

 their tubes, the horny polypary ex- 

 tending only to their bases. The 

 polypites are somewhat conical in 

 shape, the mouth being placed at the 

 apex of the cone, and they are furnished with two sets of ten- 

 tacles. One set consists of numerous short tentacles placed 

 directly round the mouth, the other is composed of from 

 thirty to forty tentacula of much greater length arising from 

 the polypite about its middle or near its base. Near the in- 

 sertion of these tentacles the generative buds are produced at 

 proper seasons. In Eudendrium (the branched pipe-coral- 

 line) the essential structure is much the same as dn Tubularia, 

 but the hydrosoma is now truly compound, consisting of a 

 number of non-retractile reddish polypites, united by a cceno- 



* ChUine is a sxibstance which is nearly allied to horn, but is distinguished from it by 

 the fact that it is not soluble in caustic potash. 



FIG. 14. Fragment of Tiibularia 

 indivisa, natural size. 



