128 Bibliograpfdcal Notices. 



the notice of our readers, and have given them, as best we could, a 

 knowledge of the kind of information which it contained, and of the 

 manner in wliicli that information had been communicated. But an 

 editor, alas ! like still greater potentates, is dependent on his allies, 

 and not until now have we succeeded in obtaining that co-operation 

 and assistance which the fulfilment of our design required. We shall 

 therefore endeavour by a careful analysis, and by extracts more copious 

 than we generally give, to make amends to our readers for our delay in 

 making them acquainted with a work of such originality and value ; 

 one which has elicited the encomiums of Professor Agassiz, who, 

 among living naturalists, is perhaps the one best qualified to appre- 

 ciate its merits*. 



The following passages from the introduction state precisely what 

 portion of the animal kingdom is treated of under the term Echino- 

 dermata : — 



"The Echinodermata constitute one of the three great classes into which 

 the Radiata are divided. The Radiate type presents us with animals which 

 eitlier luive their parts arranged in a ray- like manner round a common 

 centre, or have their bilaterality so modified as to give them a star-Hke form. 

 The Zoophytes, the Medusae, and the creatures to which this vohune is de- 

 voted, constitute the type. The Echinodermata are most highly organized, 

 mucli more so than the Polypes ; they are almost all free animals, creeping 

 about at the bottom of the sea; and as the greater number of species are 

 covered with a coriaceous skin, which is commonly strengthened by calca- 

 reous plates or spines, they have derived their general appellation from that 

 remarkable charactei', which at once distinguishes them from the Medusae, 

 free swimming animals of die most dehcate and membranous texture." 



" The system most characteristic of the Radiate type is tlie Aquiferous, 

 or apparatus for a water circulation ; indeed, it can scarcely be said to exist 

 in any of the other types. It is chiefly developed in the Arachnodermata and 

 Echinodermata, and in the last is intimately connected with the movements 

 of the animals ; for it is by means of this water circulation that the suckers 

 or cirrhi are enabled to act as organs of progression, lu many species of 

 the most typical group, that oi Eclnnidce, we find a portion of the dermato- 

 skeleton turned in, as it were, to form arches for the protection of the water- 

 canals, thus evidencing their great importance in those creatures. Among 

 the Annelidoiis Echinodermata, however, the aquiferous system seems alto- 

 gether to disappear. 



" On the modifications of this characteristic system, its presence or ab- 

 sence, and its combination with the tegumentary system for purposes of mo- 

 tion, I have founded my arrangement of the Echinodermata. I look upon 

 the Echinodermata and Arachnodermata as two parallel groups, and hold it 

 as a law that the divisions of parallel groups should be based on a common 

 principle." 



In accordance with tliis view the author proposes the following ar- 

 rangement : — 



Order I. Pinnigrada. Crinoide^ — First appearance of cirrhi, spring- 

 ing from brachial membranes, which, with the true arms, form 

 the organs of motion. 



See Ann. Nat. Hist. vol. ix. p. 189. 



