2 BRITISH PALAZOZOIC FOSSILS. [Zoopuyra. 
In the lamelliferous corals the number of the lamellze mostly corresponds with that of the tentacles, and 
as they are generally believed to be nearly constant in number in adult individuals, they afford very valuable 
characters for the discrimination of species. Lamellie only exist in the two higher orders, and extend from the 
stomach to the outer wall; they are connected with the generative system, the broad lamell: having usually 
a great convoluted spermatic vessel attached to its edge, and the sides of the others are loaded with clusters 
of ova; in some Alcyonaria (in which the lamellze are membranous and eight in number) the same lamella is 
oviferous above and spermatic below, or two are spermatic and the other six are oviferous. These spermatic 
cords were considered biliary ducts, till the American naturalists recently found spermatozoa in them. The 
ova either escape through a small opening in the bottom of the stomach into the sea by the mouth, or some 
of them are developed inside, and bud out through the side of the parent; the buds either fall off and become 
separate individuals, or are retained forming branched compound animals, always according to a definite mode 
of growth, and the angle of branching being often so constant as to assist in defining the species. 
The modes of budding, as defined by Mr Dana, are lateral or terminal. The terminal or disk-budding 
begins by the animal forming two or more new mouths to the one stomach, being the true fissiparous generation. 
The lateral disk-budding should be carefully distinguished, for in it, it is only one of the ova which grow 
out through the side of the disk, and the second mouth has a separate stomach of its own hanging into 
the ovarian cavities of the old one. Acrogenous growth is the upward extension of the tip of the branches ; 
prolate growth is the production of lateral buds from the lower part, so that great flat expansions are produced 
(as in some Caryophyllide), or by extension of the upper part from disk-budding (as in the Astreadw). The 
spiral-budding, or cumulato-ramose growth, is seen in the Madrepores, where each branch is composed of a great 
central parent polyp (forming the perforated apex), surrounded by a whorl of spiral buds. In all the coral- 
bearing polypes there is a constant death below, leaving only the tips of the cells alive; and in certain cases 
those die periodically, leaving a germ to grow from the old centre, forming cup-shaped rings of growth, 
as seen in our figure of Strephodes multilamellatum. An intermittent retraction of the base of the stomach 
gives rise to the transverse partitions of Oyathophyllum and Favosites. 
This Class contains three Orders—Ist, Hydroida* ; 2nd, Zoophytaria ; 3rd, Zoantharia. 
Ist Ord. Hyproma (Johnston.) 
= Sertulariens (7. Edw.) = Hydrozoa (Owen) = Nudibrachiata (Yarre.) > Polypiaria (Blainville). 
The Polypes of this Order are rarely single, locomotive, and naked (as the Hydra); more usually compound 
and inclosed in a horny, tubular sclerenchyma or sheath, which is generally branched, jointed by interruptions of 
growth, and fixed at the base to submarine bodies ; always destitute of internal vertical strize or lamellz ; mouth 
surrounded by a series of rough, rigid, filiform tentacles, without cilia ; digestive cavity hollowed in the granular 
parenchyma of the body, without membranous walls, having but the one opening t, and no intestine. The young 
sprout from the side of the parent by lateral budding, or are developed in external vesicles connected with 
it; the former occurs in the naked Hydra, in which at intervals cellular male and female organs are 
developed, sometimes in different individuals, more commonly both in the one creature; the impregnated 
ova mostly escaping through the mouth, but some being retained, grow out like buds from the parent. In 
the compound species, with the horny, tubular integument, the young buds adhere permanently to the parent, 
forming branched polypidoms of a peculiar pattern for each species; but, in addition to these, peculiar ovi- 
gerous vesicles are developed at particular seasons on some definite parts of the stem containing the true 
* Although I think the recent admirable researches of Prof. Agassiz, on the living Naked-eyed Medusw of the shores 
of Massachusetts, nearly settle the question of the Hydroid Polypes being only the larval state, or alternate generations 
of such free Meduse as Sarsia and Tiaropsis, yet I prefer, in a work like the present, leaving them in their old 
systematic place till we have the whole question before us, by the publication of his observations on the first stages 
of the metamorphosis. 
{ Corda imagined a small pore near the terminal sucker to be an anus, but the food is seen to be rejected by the mouth. 
