CCELENTERATA : HYDROZOA. 



been treated at some length, so as to apply to the remaining 

 Hydroida, we shall now give a brief description of the two 

 leading types of structure exhibited by the order. 



Eudendrium, a genus of the Cory- 

 nida, which is not uncommonly found 

 attached to submarine objects, usually 

 in tolerably deep water, may be taken 

 as a good example of the fixed and 

 composite division of the order. The 

 hydrosoma consists of numerous poly- 

 pites, united by a ccenosarc, which is 

 more or less branched, and is de- 

 fended by a horny tubular polypary. 

 The polypites are borne at the ends 

 of the branches and branchlets, and 

 are not contained in " hydrothecae," 

 the polypary ending abruptly at their 

 bases. The polypites are non-retrac- 

 tile, of a reddish colour, and provided 

 with about twenty tentacles, arranged 

 round the mouth in a single row. 

 Tubidaria (fig. 16) is very similar to 

 Eudendrium, but the hydrosoma is 

 either undivided or is very slightly 

 branched. The hydrosoma consists 

 of clustered horny tubes, of a straw 

 colour, and not unlike straws to look 

 at; hence the common name of pipe- 

 coralline given to this zoophyte. 

 Each tube is filled with a soft, semi-fluid reddish ccenosarc, 

 and gives exit at its distal extremity to a single polypite. The 

 polypites are bright red in colour, and are not retractile 

 within their tubes, the horny polypary extending 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 tentacles. One set consists of 

 numerous short tentacles placed directly round the mouth; 

 the other is composed of from thirty to forty tentacles of 

 much greater length, arising from the polypite about its middle 

 or near the base. Near the insertion of these tentacles the 

 generative buds are produced at proper seasons. 



Coryomorpha nutans may be taken to represent those Cory- 

 nida in which there is no polypary and the hydrosoma is simple. 

 It is about four inches in length, and is fixed by filamentous 

 roots to the sand at the bottom of the sea. It consists of a 



Fig. 16. Corynida. Fragment 

 of Tubularia indivisa. Natu- 

 ral size. 



