KEPORT ON THE HYDROIDA. 17 



branches. It is polysiphonic or fascicled, when it is composed of several mutually 

 adherent tubes ; monosiphonic when consisting of a single tube. In some species the 

 cavity of its perisarc is constricted at intervals by annular ridges or imperfect septa — 

 intracauline ridges. 



Hydrocladia. — The hydrotheca-bearing ramuli — almost always the ultimate ramuli 

 — of the hydrocaulus in the Plumularidae. 



Eachis. — That portion of the hydrocladium which supports the hydrotheca3. That 

 portion of the phylactocarp which supports the costse or their equivalents. 



Internode. — The part of the hydrocaulus which intervenes between any two 

 consecutive joints. 



Ccenosarc. — The common organised fleshy portion of the hydrophyton ; the living 

 bond by which the zooids are organically united to one another. 



Nematophores. — Peculiar bodies developed in certain genera from definite points of 

 the hydrosoma, and consisting of a chitinous receptacle with protoplasmic contents, in 

 which thread-cells are usually immersed. They are eminently characteristic of the 

 Plumularidse. 



GoNOPHORE. — The ultimate generative zooid which gives origin directly to the 

 generative elements— ova or spermatozoa. 



GoNANGiUM. — An external chitinous receptacle within which in the calyptoblastic 

 genera the gonophores are developed. 



Blastostyle. — An extension of the coenosarc throuoh the axis of the gonangium in 

 the form of a fleshy column from whose sides the gonophores are developed as buds. 



AcROOYST. — An external sac which in certain hydroids is formed on the summit of the 

 gonangium, where it constitutes a receptacle into which the ova are discharged in order 

 to pass within it through some of the earlier stages of their development. 



Phylactocarp. — A part of the gonosome specially modified for the protection of the 

 gonangia in certain genera (phylactocarpal) of the Plumularidee. 



CoRBULA. — A form of phylactocarp constituting a basket-shaped receptacle which 

 encloses groups of gonangia in certain phylactocarpal Plumularidse. 



CosT^. — ^Rib-like appendages which form part of the protective arrangement in 

 certain phjdactocarps. 



Gymnoblastic. — The condition of a hydroid when no external receptacle (hydrotheca 

 or gonangium) invests either nutritive or generative buds. 



Calyptoblastic. — The condition of a hydi-oid when an external protective receptacle 

 (hydi'otheca or gonangium) invests either the nutritive or generative buds. 



(ZOOL. CHALL. ESP. — PART XS. 1S83.) U 3 



