226 Literatur der Pantopoden. 



und Bau der Gruppe und schliesst sich mehr den Auffassungen Savigny's als Latreille's an. 

 Er schliesst mit folgenden Sätzen: 



Some naturalists cannot coineide in this Suggestion, because of the great simplicity of the anatomy 

 of the Pycnogonidae, which is very inferior to that of the Crustacea. The simplicity of their strueture 

 must he admitted ; the alimentary canal appears to he a straight intestine extended hetween the mouth 

 and anus, with some lateral expensions or coeca; and the circulating System is probably reduced to a single 

 vessel which oecupies the centre of the thoracic Segments , and sends a branch to each member or limb, 

 in which the blood has an irregulär movement, mit cannot be said properly to circulate. The rest of their 

 anatomy is unascertained. Hut the avgument hence deduced is one which will equally forbid their 

 admission among the Arachnides, for the typical spiders are little less highly organized then the typical 

 Crustaceans ; and M. Edwards has shown that, by assuming anatomical characters as the basis of Classifi- 

 cation, the most unnatural combinations wordd be the residt, so that even they who have advocated the 

 superiority of these characters, have found an adherence to their principles quite impracticable in the 

 Classification of avertebrate animals. It is a better and safer method to arrange these animals in as many 

 groups as there are distinctly recognizable series formed by the successive simplification or degradation of 

 each distinet organism. In this way we are not arrested by difl'erences of anatomical strueture, when these 

 are confined to mere differences of complexness ; and, in the instance of the Crustacea, we attach to the 

 class all those species whose general organism, however simple, has no deviations incompatible with that 

 of the types of the class, but which simplicity is, if we may so speak, the result of an arrest to its 

 development, and recalls by its similarity, the transitory conditions through which the most perfect con- 

 stituents of the class have passed during the continuance of their embryonic life. To proeeed thus may 

 seem to be acting contrary to the recognized principles of natural Systems, and one is apt to be startled 

 at a proposal to gather together in one category animals which breathe by gills or branchiae, with others 

 which have no special organs for the Performance of that important fnnetion, being reduced to respire by 

 the skin; - - animals which have a heart and a very complicated vascular System, with others which have 

 no heart and no very distinet vessels : — animals which have a powerfully armed mouth and greatly 

 developed ehylopoetie viscera, with others which are sucklings, and whose intestines are fitted for the 

 digestion of no solid food. Hut these difficulties disappear when we discover how much these organs, so 

 influential in the higher animals, are modified before they entirely disappear in these less perfect beings ; — 

 how they become by little and little rudimentary previous to their obliteration, a loss which is then little 

 feit, and is not aecompanied with any essential change in the type of their Organization. Branchiae, for 

 example, become rudimentary and disappear, to be replaced and have their funetions performed, l)y the 

 common integuments in some Crustaceans, almost alike, in other respects, to others which are furnished 

 with these organs in a State of high development , and that too without any notable modification in the 

 other great Systems. The blood- vessels cease to have distinet parietes, and exist no longer excepting as 

 simple lacunae in some Crustacea, which it is impossible to separate from other animals of the same class 

 having a very complete vascular System ; and the heart becomes rudimentary. and perhaps even completely 

 disappears, althongh nothing has oecurred in the body generally to reveal its absence. These facts have 

 induced M. Edwards rightly to place in the class Crustacea not only the articulated animals with jointed 

 feet, having a complete circulation and branchiae — the characters which are usually assigned to it — but 

 also all those which. formed on the same general plan, are more or less imperfect, and in one sense 

 degraded. The group thus formed will be more difficult to define, but better this than that it should be 

 circumscrihed by arbitrary limits. 



Class Crustacea — Sub-class Haustellata. 



Order Araneiformes M. Edwards. 



(Poclosomata Leach. — Pycnogonides Latkeille.) 



Character: — Animals crustaeeous, araneiform: head rostrate, tubulär, the mouth terminal, simple: 

 thorax linear, of 1 sub-equal Segments, the anterior with 1 simple eyes placed on a dorsal tubercle: legs S, 

 cxcliisivc of the auxüiary organs to the head. very long proportionally, ambulatory, i'aptorious, 8-jointed: 



