J. D. "Dana on the Classification of Crustacea. 



19 



and they are less fitted for self-preservation. The large Dromia 

 picks up a waste shell, and by means of its hind legs, lifts it 

 over its body for protection, and the Pagurus finds shelter in the 

 water-worn univalves of a coast. 



The degradation pointed out, is hence, not merely a variation 

 in the position and size of certains organs, but an actual deterio- 

 ration in rank and intelligence. 



Other minor points exhibiting difference of grade, might be 

 mentioned: but they have already been subjects of remark. 

 We state here only one — the character of the fingers of the 

 large hands. In the higher species, these fingers are pointed ; 

 in a grade below, in some groups, they have a spoon-like ex- 

 tremity. This excavate form is often more perfect in young in- 

 dividuals than in adults, which is one evidence that it is in fact 

 proof of inferiority. By this mark we learn that the Chlorodince 

 are of lower grade than the Xanthince ; the Paguri, than the 

 Bernhardt; the Mithracidce, than the Maiadce, etc. 



Let us now pass to the Macroura. In the typical Macroural 

 species, the antennae, instead of being minute, with the inner 

 retractile, are long exsert organs, and the outer have a large 

 plate as an appendage at base ; the eyes are without sockets ; 

 the outer maxillipeds are pediform, and do not closely cover the 

 outer mouth organs ; the abdomen is often longer than the rest 

 of the body, and has its six regular pairs of appendages. All 

 these points show a still further relaxing of the centralization or 

 cephalization of the species. There is an elongation of the 

 parts anterior to the mouth, and also of those posterior, and 

 this elongation of the two extremities is approximately propor- 

 tional to the relative dimensions of the corresponding parts in 

 the Brachyura. If we were to draw out an ovoid with the rela- 

 tive length and breadth of a Macroural cephalothorax, and place 

 its focus so as to correspond with the position of the posterior 

 margin of the epistome, in a manner like that proposed for the 

 Maia among Brachyura, the ovoid for the Macroura would be 

 very narrow, and the focus or centre proportionally farther from 

 the front than in the Brachyura. 



In following down the degradation of the Brachyura to the 

 Anomoura, we have found the posterior legs becoming abbre- 

 viated, and the whole structure in its aspect imperfect. But, in 

 the typical Macroura, there is nothing of this seeming imperfec- 

 tion. The legs are all fully formed ; the animals are exceed- 

 ingly quick in their motion, instead of being sluggish ; and 

 every organ is apparently in its most perfect state for the uses 

 of the system to which it is tributary. We should, therefore, 

 understand, that the process of degradation, alluded to above, is 

 not one actually passed through in the system of creation ; for 

 by its progress we should never reach the Macroural structure ; 



