HOMOLOGY OF THE SKELETON. 11 



as there are spaces in each ray : in the angle at the vertex of this the osseous column is 

 fastened to the superior integument, which appears to be perforated. The texture of 

 Asterias rosacea is likewise entirely osseous. 



The rays in the OpJiiurce have compressed vertebrae, orbicular, without any per- 

 foration, and with articular faces, as well as two furrows, • one upwards and the other 

 downwards. In the neighbourhood of the mouth, where they get larger, they support 

 the two branches, of which the denticulated jaw is composed towards its end, and in A. 

 cordifcra [Ophiolepis ciliata) towards its basis. On the sides of the radii in A. ophiura 

 [Op/iiolepis scolopendrica) is noticed a couple of lamellated bones which are connected with the 

 radii and with the epidermis : in case of this epidermis being deficient, as in A. cordifera 

 {OpMolepis ciliata), these sca'y bones are connected with its osseous and imbricated crust. 



Echitiaster echinophora has, moreover, many small bones, still smaller in TJraster 

 rubens, which are articulated with the very small bones constituting the superior surface 

 of the body. They correspond likewise with the axis of the moveable tubercles, acumi- 

 nated in E. echinophora, rounded in Asterias Savaresi, and surrounded by the epidermis ; 

 from these shoot out several muscular fibres, directed towards the respective osseous 

 pedicellariae, which, when looked upon through a magnifying lens, appear either to have 

 an acuminated shape, or to be compressed and entirely rounded like the bill of a goose. 

 Each pedicellaria is composed of two osseous, articulated pieces, fixed on a common basis 

 of the same description. They enjoy the faculty of adhering to adjacent bodies, and keeping 

 closely adhesive. 



The small osseous chalices (or paxillse) of Astropecten araniiacus, A. bispinosa, &c., are 

 differently constituted. Each of these is a cylinder fastened at the bottom by means of 

 strong muscular bands, the fibres of which have several intervening holes ; it ends at the 

 top in a convex shape by many cylindrical pieces, distributed according to a double series, 

 with internal articulations, and provided in the middle with a conical piece, excepting in 

 A. arantiacus alone. It would be useless to enter into further minute details, which may 

 be more easily traced out by an inspection of the purposely drawn-out figures in the tables. 



De Blainville^ says, the star-fishes have still a particular disposition of the external 

 envelope, the dermis is more distinct than in the urchins ; we see better that solid and 

 calcareous parts are developed in its interior. These parts form spines or scales 

 more or less immoveable, and which present dispositions proper to each of the groups of 

 this order. 



In the Asterias, properly so called, that is to say, in the species in which the body is 

 not provided with appendages, but which are divided more or less deeply into rays hollowed 

 out inferiorly by a groove which extends throughout their entire length ; the superior parts 

 have the skin sometimes soft, and oftener solidified by a greater or less number of irregular 

 pieces arranged in a reticulate manner. 



They are sometimes almost smooth, but in general are bristled with tubercles of 



1 De Blainville, 'Organisation des Animaux,' p. 213. 



