DEVELOPMENT OF ANTEDON (COMATULA, LAMK.) EOSACEUS. 



703 



nothing else than non-differentiated sarcode — which I have shown {loc. cit.) to be the 

 essential constituent of the skeleton in every type of the Class Eciiixodermata. The 

 character of this reticulation is best seen either in very thin sections of any portion of 

 the skeleton (Plate XXXV.), or in that curiously-inflected cribriform lamina (Plate 

 XXXIII. figs. 9-11) which I have termed the " rosette" (§ 35). This is the only part 

 of the skeleton of the adult Antedon in which the reticulation lies all in one plane ; 

 but, as Professor Wyville Tiiomsok has already shown, even its most solid portions, 

 such as the First Radials, make their first appearance in the same form of cribriform 

 lamellaj (Plate XLI. fig. 1) ; and whilst these lamella? increase in superficial dimensions 

 by the extension of the reticulation from their margins, they are augmented in thickness 

 also by an extension of the reticulation from their inner surfaces into the animal 

 basis in which they are imbedded. — When a portion of the skeleton, either from a fresh 

 or from a spirit-specimen, is subjected to the action of dilute nitric or hydrochloric acid, 

 by which the calcareous network is dissolved away, a continuous film of pellucid sarcodic 

 substance is left, presenting no other trace of structure than in being studded at regular 

 intervals mth- minute granular spots (Plate XLIII. fig. 1). The precise accordance of 

 these spots, both in size and distance, with the meshes of the reticulation, leaves little 

 room for doubt that whilst the pellucid sarcodic substance is the basis of the calcified 

 network itself, the granular glomeruli occupy its interspaces. From the behaviour 

 of this basis-substance with reagents, it seems to correspond closely with the plasma 

 of the higher animals and with the sarcode of the lower ; the pellucid substance being 

 apparently albuminoid in its nature, whilst the granular spots are partly composed of 

 oil-molecules. 



18. The pieces of the skeleton are held together by Ligaments, which consist of 

 minute well-defined fibres bearing a strong resemblance in aspect to those of the Yello^v 

 Elastic substance, but not (like them) capable of resisting the action of strong acetic 

 acid. The diameter of these fibres (Plate XLIII. figs. 3, 3a) does not exceed - ^ 5 q „ „ of 

 an inch ; they usually run straight and parallel, but sometimes cross each other obliquely. 

 Their attachment to the pieces of the skeleton which they connect is peculiarly firm ; and 

 this firmness is found to depend, when we examine portions of the skeleton that have been 

 subjected to decalcification, on the passage of the fibres into the basis-substance of the 

 skeleton itself [^ 27) ; much as the fibres of ligaments attached to bones are continuous 

 with their fibroid basis, or as the fibres of tendons attached to cartilages pass into their 

 intercellular substance. From the position and action of the ligaments connecting the 

 pieces of the skeleton of Antedon, I think it is clear that some of them are simply inter- 

 articular, having for their function to tie these pieces together, but allowing a certain 



genus. And having myself independently discovered it, I was at tho same period engaged in tracing it through 

 all the leading types of tho class Echinodermata, fossil as wcU as recent ; the results of which inquiries were 

 made kno-ivn in the Annals of Natural History, vol. xii. (1843) p. 377 ; and more fuUy in the Eeports of the 

 British Association for the year 1847. 



MDCCCLXVI. 5 D 



