126 



COELENTERATA. 





into medusae which become free-swimming, or medusoids which are imperfectly 

 developed medusae and do not become free. These medusae and medusoids are 

 called^ the 'yono2)liores because the gonads are contained in them. A phancro- 



codonic gonophore is a free - swimming 

 medusa, and is sometimes termed a 

 planoblast. ; an addocodonic gonophore is 

 a medusoid, and is sometimes called a 

 liedriollast. Sometimes the gonophores 

 are budded only from special hydranths, 

 which are then modified by the absence 

 or diminution of size of the tentacles 

 and mouth. Such a proliferous hydranth 

 is a blastostyle. In the forms with 

 hydrothecae, the hydrotheca of the 

 blastostyle forms a chitinous capsule 

 enclosing the blastostyle and gonophores ; 

 it is called the gonangium or gonotheca 

 (Figs. 110, 114). Colonies with gonangia 

 are called calyptoblastic ; those without 

 f/ymnoblastic. The word zooid or ^?ers<m 

 is sometimes applied to any individual 

 of a colony, whether hydranth, gono- 

 phore, or blastostyle, etc. Tropliosome 

 means the entire assemblage of zooids 

 which are concerned with the nutrition 

 of the colony, i.e., all the hydranths; 

 gonosome the entire assemblage of zooids 

 which are concerned with the sexual 

 reproduction of the colony, i.e., all the 

 gonophores. A dactylozooid or spiral 

 zooid is a hydranth without or with 

 reduced mouth and tentacles, specially 

 developed in some genera (Hydractinia 

 and Podocoryne, Fig. 108) for defensive 

 purposes. A ncmatopliorc (maclw -polyp, 

 giiard- polyp, sarcostyle) is a special 

 stalked projection of the coenosark found 

 in the Plumularidac (Fig. 111). It con- 

 sists of ectoderm, which contains thread- 

 cells and is highly amoeboid, and of a 

 solid axis of endoderm ; the whole is en- 

 closed in a theca (sarcotheca) of perisark. 

 Nematophores are probably nutritive, 

 catching food as an Amoeba does, by 

 the pseudopodia of their ectoderm. 



Eydrodadium is a special term applied 

 to the hydrotheca - bearing branches 

 (ramuli) of the coenosark of Plumula- 

 ridae. Phylactocarps are specially modified liydrocladia bearing gonangia as 

 well as nematophores and sometimes hydrothecae ; they often develop protective 

 branches the costae which form the walls of an open basket-work and enclose 



/[,-*-' 



FIG. 111. Aniennulf-maantennina. Branch 

 (hydrocladium) of colony with hydranths 

 and nematophores (from Chun, after All- 

 man), p extended, p 1 retracted hydranth ; 

 11, tig nematophores ; r coenosark (hydro- 

 cladium). 



