CCELENTERATA : HYDROZOA. 



89 



as in Hydractinia and Dicoryne. These gonoblastidia are 

 processes from the body-wall or coenosarc, which closely re- 

 semble true polypites in form, but differ from them in being 

 usually devoid of a mouth, and in having shorter tentacles. 



As regards the development of the Corynida, the embryo is 

 very generally, though not always, ciliated at first, and be- 

 comes developed into a hydra-form polypite, which fixes itself 

 to some foreign body, and then (if not belonging to one of the 

 simple forms) proceeds to produce by gemmation the com- 

 posite adult. The development of the Corynida (as well as 

 that of the Sertularida and Lucernaridd) obeys the general law, 

 that the new polypites are developed at, or near, the distal end 

 of the hydrosoma ; so that the distal polypites are the youngest, 

 the reverse of this obtaining amongst the oceanic Hydrozoa, 



The subject of the reproduction of the Corynida having 

 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 ob- 

 jects, usually in tolerably deep 

 water, may be taken as a good 

 example of the fixed and composite 

 division of the order. The hydro- 

 soma consists of numerous polypites, 

 united by a coenosarc, which is more 

 or less branched, and is defended 

 by a horny tubular polypary. The 

 polypites are borne at the ends of 

 the branches and branchlets, and 

 are not contained in " hydrothecse," 

 the polypary ending abruptly at their 

 bases. The polypites are non- re- 

 tractile, of a reddish colour, and 

 provided with about twenty ten- 

 tacles, arranged round the mouth in 

 a single row. Tubularia (fig. 16) is 

 very similar to Eudendrium, but the 

 hydrosoma is either undivided or is 

 very slightly branched. The hydro- 

 soma 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. 



— Corynida. Fragment of 

 "Tubularia indivisa, natural 

 size. 



