702 DE. "W. B. CAEPENTEE ON THE STEUCTUEE, PHTSIOLOG-T, AND 



were placed, \nih a like assemblage of specimens, a sufficient number of rough stones 

 to afford them all a basis of attachment, they would be all found in the morning in a 

 state of full expansion, with every appearance of health and vigour. Hence I feel 

 justified in concluding that in these animals the Respiratory function can only be 

 effectually performed in a pure well-aerated medium, and that the free exposure of the 

 arms to that medium is no less required. I may add, further, that the intermixture of 

 a small proportion cither of fresh-water or of glycerine with the sea-water in which 

 Antedons are immersed, is very speedily fatal to them. — It will be showTi in the Second 

 Part of this Memoir that, besides the so-called " ambulacral " canal with its tentacular 

 extensions, each Arm and each Pinnule contains an afferent and an efferent canal, in 

 which the nutritive fluid is exposed to the aerating influence of the surrounding medium. 

 And that this Branchial function is shared by the Tentacular apparatus also, would 

 appear alike from the negation already given to its supposed prehensile activity, and 

 from its own structure and relations, as will be fully shown hereafter. Such a double 

 provision for the function of Eespiration has been shown by M. DE Quatrefages to be 

 very common among the Annelida. 



16, From the foregoing observations and the reasonings based upon them, we seem 

 justified in regarding the following as probable conclusions: — 



1. That Antedon, so far from being an active free-swimming animal, has the same 

 fixed habit in its mature attached as in its earlier unattached condition; so that in 

 regard to its general manner of life, it is not less entitled in the later than in the earlier 

 stage of its existence, to rank as a type of the Crinoids generally. 



2. That neither the Arms and their ordinary Pinnules, nor those elongated basal Pin- 

 nules which arch over the central disk, have any prehensile action, or any direct con- 

 cern in obtaining supplies of food. 



3. That the ordinary Pinnules are specially related to the function of resjnration, in 

 virtue alike of theh proper Branchial canals, and of the ambulacral canals and the 

 tubular tentacula with which they are furnished. 



4. That the elongated basal Pinnules, in which the tubular tentacula are wanting, 

 are rather related to the function of sensorial jJrotectiou than to that of prehension. 



IV.—STRIJCTIJKE OF THE SKELETON. 



1. Of the Skeleton generally, with its Ligaments mid Muscles. 



17. The component pieces of which the Skeleton of Antedon is made up, alike in its 

 adult condition and in every previous phase of its existence, present a remarkable 

 accordance with each other in elementary structure ; consisting throughout of that 

 calcareous reticulation' — formed by the calcification of an animal basis that seems 



' This reticulation appears to have heen first noticed by Professor J. IIuller in 1841 (Cher den Bau des Poi- 

 tacrim(s) as constituting the skeleton of tho recent Fcntaciimis of the Antilles. It was more fuUy described by 

 Professor YAuaJTiir in 1842 (Anatomie du genre Echiniis) as presenting itself in the shell and spines of that 



