Miscellanea Zoologica. 375 



breathe by gills or branchiae, with others which have no special or- 

 gans for the performance of that important function, 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 distinct vessels ; — animals which have a powerfully armed 

 mouth and greatly developed chylopoetick viscera, with others which 

 are sucklings, and whose intestines are fitted for the digestion of no 

 solid food. But 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 obli- 

 teration, a loss which is then little felt, and is not accompanied with 

 any essential change in the type of their organization. Branchiae, 

 for example, become rudimentary and disappear, to be replaced and 

 have their functions performed, by the common integuments in some 

 crustaceans, almost alike, in other respects, to others which are fur- 

 nished with these organs in a state of high developement, and that 

 too without any notable modification in the other great systems. The 

 blood-vessels cease to have distinct parietes, and exist no longer ex- 

 cepting 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, although nothing has occurred in the 

 body generally to reveal its absence. These facts have induced M. 

 Edwards rightly to place in the class Crustacea not only the arti- 

 culated animals with jointed feet, having a complete circulation and 

 branchiae — the characters which are usually assigned to it, — but al- 

 so all those which, formed on the same general plan, are more or 

 less imperfect, and in one sense degraded. The group thus form- 

 ed will be more difficult to define, but better this than that it should 

 be circumscribed by arbitrary limits. * 



Class CRUSTACEA— Sub-class C Haustkllata. 

 Order, Araneiformes, M. Edwards, 

 (Podosomata, Leach. — Pycnogonides, Latreille.) 

 Character. — Animals crustaceous, araneiform : head rostrate, tu- 

 bular, the mouth terminal, simple : thorax linear, of 4 sub-equal 

 segments, the anterior with 4 simple eyes placed on a dorsal tuber- 

 cle : legs 8, exclusive of the auxiliary organs to the head, very long 

 proportionably, ambulatory, raptorious, 8-jointed : abdomen rndi- 



* Hist. Nat. des Crust, i. 227-8: 



