J. D. Dana on the Classification of Crustacea. 7 
and they are less fitted for self-preservation. '"l'he 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 1n 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 
arge hands. In the higher species, these fingers are pointed; 
in a grade below, in some groups, they have a spoon-like ex- 
tremity. 'lhis 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 CAlorodinc 
are of lower grade than the XXanthine; the Paguri than the 
Bernhardi; the Mithracide, than the Maiadce, etc. 
Let us now pass to the Macroura. In the typical Maeroural 
species, the antennse, 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 
eephalization of the species. 'lhere 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 1n 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- 
ton. 'The legs are all fully formed ; the animals are exceed- 
ingly quiek 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 ; 
