700 RADIATA 



Section A. Po.ypiaoms calcareous ; the cells tubular willi a round terminal aperture uncovered by an operculum. 

 Family 1. Tiilndiporida: Polypidoms multiform, massive or crustaceous. 

 Family 2. Crisiadtv. Polypidoms confervoid, jointed. 

 Section B. Polypidoms calcareous or membrano-calcareous, multiform, composed of oblong or oviform cells, 

 whose subterminal aperture is closed by a membranous fold or operculum. 



Family 3. Eucratiadce. Polypidoms branched in a confervoid manner ; cells oblong ; no ovarian capsules. 

 Family 4. CcUeporida'. Polypidoms massive or crustaceous, composed of ovate cells in juxta-position, the 



aperture terminal, often furnished mth a globular capsule. 

 Family 5. Escharida'. Polypidoms multiform, composed of oblong sub-quadrangular cells, disposed in a 

 semi-alternating series ; the cells conjunct, horizontal to the plane of axis, with a subterminal or 

 lateral aperture, usually covered with an ovarian capsule. 

 Section C. Polypidoms sponge-like, tleshy, polymorphous ; the cells irregular in disposition, immersed, with a 

 contractile aperture ; no external ovarian capsules. 

 Family 6. HalcyoneUea. 

 Section D. Polypidoms confervoid, horny, fistular ; the polype-cells free. 



Family 7. Ve$iaular'>adce. Body of the Polype separate from the parietes of the cell, which is deciduous. 

 Family 8. PcdiccUince. Body of the Polype adnate to the cell. 



Oeder II.— HIPPOCKEPIA. 

 Lacustrine or natives of fresh water. Polypes compound, the mouth surrounded with ciliated retractile teiita- 

 cula, interrupted or depressed on one side, so as to assume a crescentic or horse-shoe form ; ova unciliated. 

 Section A. Polype-mass floating. 



Family 1. CristatellidcB. 

 Section B. Polype-mass rooted. 



Family 2. Plumatellida: Poiype-mass massive or confervoid ; inarticulate. 

 Family 3. PaJudicellid(e. Polype-mass confervoid, jointed. 

 It would seem that with the Bryozoa should be associated the very curious group of Foraminifera, placed by 

 Cuvier among the Cephalopoda. The structure of the animals has not been yet made out, however, with sufficient 

 precision to enable their exact position in the zoological scale to be determined. 



The Bryozoa are diffused through all latitudes, and they appear to have existed at a very early period of the 

 earth's history ; many of the (so-called) corals of the palseozoic series belonging to this division. Their massive 

 stony structures would seem to have been formerly more abundant in our own seas than they are at present ; 

 whole reefs having been produced by their growth, as they are in the tropical seas by the growth of the existing 

 corals of the lamcUifoi-m kind presently to be described. 



ANTHOZOA. 



The Anthozoa, or true Polpyiy are distinguished from the preceding by the perfect radial symmetry 

 of their internal structure, as well as of their external conformation. Their nervous system has not 

 been clearly made out ; but there can be no doubt that, if it really exist in a distinct condition, it 

 forms a ring surrounding the mouth. The digestive cavity has no 

 intestine nor anal orifice ; but in many compound Polypefera it is 

 prolonged into the interior of the mass, and joins a system of canals by 

 which the stomachs of the several Polypes are connected with each 

 other. The tentacula are never clothed with cilia. The class may 

 be divided into the orders Hydroida, or Hydraform Polypes ; 

 Helianthoida, or Actinifonii Polypes ; and Asteroida, or Alcyo- 

 nian Polypes. By some, however, the two latter orders are regarded 

 as forming one group, equivalent to the Hydroida. 



Oedee I.-HYDROIDA. 



This order is made up of simple and composite structures, of which the ny. 

 dra is the type {see text, p. 654). It is distinguished by the absence of any 

 cavity around the stomach ; the wall of the digestive cavity and the ex- 

 ternal integument of the body being merely the inner and outer layers of 

 the same membrane. The mouth is surrounded by slender tentacula, which 

 are beset with little points that seem to have a stinging power ; and by 

 Fig. u.- HviiRA ; .1, luuutli. the agency of these arms the food is grasped and conveyed into the stomach. 



They are nearly all marine, and are found in all latitudes. In some of the solitary and nearly all the com- 

 posite species, the external integument possesses a horny consistence ; and thus are formed more or less perfect 

 polype-cells, within which the body is lodged. The mode in which these structures are increased by gemination 

 frequently gives them a very plant-like aspect. The Hydra produces buds, which at first project from the side 



