TERMS USED IN DESCRIBING HYDROIDS 



Ccenosarc ("common flesh"): The fleshy axis, or organized 

 living bond, by which the zooids are organically united to one 

 another. It consists of three layers : ectoderm, endoderm, and 

 mesoderm. 



Ectoderm (" outside skin ") : The outside one of the three or- 

 ganized layers of which every hydroid is composed. 



Endoderm, (" inside skin") : The innermost layer. 



Gonangium ("seed-vessel"): The external horny receptacle 

 within which the gonophores are developed. 



Gonophore (" seed-bearing ") : A generative zooid. 



Hydranth ("water flower ") : A nutritive zooid. 



Hydrorhiza (" water-root") : The part of the colony which fixes 

 it to other bodies, like a root. 



Hydrosoma (" water-body ") : The entire hydroid colony. 



Hydrotheca ("water-receptacle"): The cup-like, horny recep- 

 tacle which protects the hydranth. 



Mesoderm ("middle skin"): A layer which lies between the 

 ectoderm and the endoderm. 



Nematophore (" thread-bearing ") : The name of peculiar bodies 

 developed in certain genera from definite points ; characteristic 

 of plumularians. 



Perisarc ("around flesh") : The transparent, chitinous shell, or 

 unorganized outer membrane of horny consistency, which covers 

 to a greater or less extent the soft parts of the colony. 



Zooid ("animal form"): One of the animals which form the 

 colony. 



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