138 DEPARTMENT OF THE NAVAL SERVICE 



ready reference. That the paper may be useful even to those who have not had 

 previous acquaintance with hydroid taxonomy, a glossary of the principal hydroid 

 terms is included. 



GLOSSARY. 



Acrocyst. An extra-capsular marsupial sac, surrounded by a gelatinous cover- 

 ing, in which development of the ova takes place in certain species. 



Actinula or actinule. A medusoid structure developed from the reproductive 

 buds in the genus Tuhularia, in which radial canals and rudimentary tentacles 

 appear but in which no mouth is present. In this structure the ova are developed 

 into the young hydroids while the structure is still attached. 



Ccenosarc. The common flesh-like substance that binds the zooids together in 

 a colony. 



Colony. A number of zooids connected together by a common coenosare. 



Coppinia. A mass formed of a close aggregation of gonangia, among which are 

 scattered modified hydro thecal, which serve as a protection for the mass. Found 

 in the Lafmidce. 



Corbula. A specially modified branch or hydrocladium which forms an euvelo])e 

 for the gonangia in certain Plumularians. 



Diaphragm. A cross partition in the hydrotheca which forms a support for the 

 base of the hydranth. 



Fascicled. A stem or branch is said to be fascicled when it consists of two or 

 more tubes closely applied. There are varying degrees of intimacy in this applica- 

 tion. The tubes may be only in loose contact or there may be cross communication^. 



Gonangium or gonotheca. The protective chitinous envelope that protects tlie 

 developing reproductive elements in calyptoblastic forms. 



Gonophore or gonozooid. A zooid specially modified for the purpose of repro- 

 duction. 



Gonosome . A collective term for all the generative zooids of a colony and 

 structures that are directly associated with them. 



Hydranth. The nutritive zooid of a colony, consisting of a digestive sac, pro- 

 boscis, mouth and tentacles. 



Hrjdrocladixim. A term applied to the hydrotheca-bcaring branchlets in the 

 Plumularidce. 



Hydrophore. A hydrotheca reduced to be saucer-shaped, — not deep enough to 

 contain the contracted hydranth. Found in the Halecidw. 



Hydrotheca. A chitinous protection for the hydranth in calyptoblastic forms. 



Tnternode. The portion of a stem or branch between two succeeding joints. 



Manubrium. The hollow pedicel supporting the mouth of a medusa. It hangs 

 freely into the sub-umbrellar cavity. 



Nematophore. A chitinous receptacle into which the defensive zooid, in the 

 form of a sarcodal process, retracts. Also applied to the receptacle and the sarcodal 

 process taken together. 



Node. A joint in the stem or branch. 



Operculum. A chitinous structure of one or more segments, that closes the 

 hydrothecal aperture when the hydranth is retracted within. 



Otocyst or lithocyst. A small sac present in the margin of the umbrella of many 

 medusa, containing refractory spherules ^vith a sensory function. 



Pedicel. The stalk supporting a hydranth or a gonophore. 



Phylactogonium. An appendage of a hydrocladium, protecting or assisting tr 

 protect the gonangia of certain Plumularians. 



