8 THE OCEANIC HYDROZOA. 



series of tentacula. In Lucernaria, the reproductive organs are developed in the same 

 way from the surface of the body on the distal side and within the margins of the disc, 

 into which the proximal division of the body is expanded. 



The mode of origin of the Lucernarian Medusa from their larvae is such, that their 

 umbrella is clearly, like that of Lucernaria itself, nothing more than a lobed expansion of the 

 body-walls, and as in Lucernaria, the reproductive organs are developed on the distal surface 

 of this expansion. The peculiar lithocysts of these Lucernariada are develojied in the deep 

 notches which mark the ends of the lobes of their umbrella. 



It will be seen presently, that in the mode of development just described, in its 

 lobed margins, and in the absence of any muscular membranous valve attached to its circum- 

 ference, the umbrella is wholly different from all other organs of natation. 



Such is the general structure of the axis of the hydrosoma, and of its anterior and 

 posterior terminations, throughout the Ilydrozoa. The different orders exhibit many 

 remarkable variations in their number, kind, and mode of attachment. To begin with the 

 last-mentioned point, it is to be observed that no regularity is traceable in the arrangement of 

 the appendages in many Corynidcs ; while in others, and in the Sertulariadce in general, the 

 branchings of the ccsnosarc and the disposition of the appendages upon it, follow a very 

 definite law, to which the regular and symmetrical forms of the organisms are due. The 

 appendages may be developed on one or on both sides of the ccenosarc. 



In such Plii/sopJiorida as possess a filiform ccenosarc {e.ff., Agalma, ForskaUa, Stephanomia), 

 the appendages appear to be always fixed to only one side of it. And even the strikingly 

 radiate disposition of some of the appendages in ForsJcalia and Stephanomia, for example, 

 does not result from their forming exceptions to this rule — for their appendages are all really 

 attached to one side of the stem only — but is due partly, perhaps, to a spiral twisting 

 of the ccenosarc, but in a much more important degree, to the manner in which these 

 appendages are forced by their peculiar form, to adapt themselves to one another. 



Whether the appendages in Phj/sophora, Velella, Porpita, and Plit/salia follow the same 

 law is not cei'tainl}' made out. 



In the Cal ijcopliorkla I am inclined to believe that all the appendages are primarily 

 attached to one side of the ccenosarc, and that the subsequent opposition of the necto- 

 calyces to one another, and of the hydrophyllia to the polypites is a secondary modification. 



The following distinct kinds of appendages exist in the Hydrozoa, and will now 

 be successively described. 1. Polypites; 2. Teniacula ; 3. Hijdrocysis ; 4. HydrofJieca ; 

 5. HydropJiyUia ; 6. Nectocalyces ; 7. Reproductive organs, consisting of Gonohlastidea and 

 Gonophores ; 8. Lithocysts. 



1. Polypites. 



By this term I understand the principal organ of alimentation of a Hydrozoon. It 

 would be wrong to call it merely a stomach, for it is much more ; and the word " polype " 

 has been, and is, used in so many senses that it is better avoided. 



Every polypite is essentially a sac, open at one end, which serves as a mouth, while at 

 the other it communicates with the somatic cavity. The oral end is usually produced 

 into a thin, flexible, and very distensible lip, whose edges are either quite simple {ILydridcE, 



