TERMS USED IN DESCRIBING HYDROIDS 
Cenosare (“common flesh”): The fleshy axis, or organized 
living bond, by which the zodids 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 zodid. 
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. 
Perisarce (“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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