4 J. D. Dana on the Classification of Crustacea. 
maxillae. Moreover, these organs are clustered into the smallest 
possible space, so that the six pairs of mouth organs hardly'oe- 
eupy more room than the first pair of legs. "The organs are all 
small, the antennz exceedingly short, the maxille small lamellar 
organs sparingly jointed. "Ihe vegetative powers of growth 
have had butlittle play. 'The inner antennz are rather large 
as regards the basal joint, which is devoted to one of the senses, 
but the rest is nearly rudimentary, and the whole is snugly 
boxed away, to be extruded at the will of the animal. "The ex- 
terior maxille (or outer maxillipeds) cover exactly the other 
pairs, and shut closely down over the mouth, like a well-fitting 
operculum to the buceal area. 
We hence learn, that the condition of highest centralization 
in Crustacea, is where the cephalie part embraces the largest 
portion of the normal structure of the cephalothorax, and the 
whole is contraeted within the smallest compass, with the least 
vegetative growts or elongation of the parts. 'The forces are 
concentrated in the more perfectly developed senses and the 
higher functions of the animal—not in giving size to the organs 
of the senses, but acuteness to the sensorial function. "The per- 
fection of the senses is evinced by the small antenne; for we 
infer therefrom, not only that the organ is exclusively an organ 
of sense, but also, that the delicacy of the sense itself is such, 
as not to require a long-jointed appendage to aid the function. 
This cephalization of the animal is farther observed in the 
structure of the rest of the thorax and the abdomen. The ab- 
domen, in the first place, 1s reduced to its minimum size. Vege- 
tative elongation is here cut short, as in the anterior part of the 
animal; and the sphere of growth has a narrow limit, owing to 
the very intensity of its concentration; and we find that the 
limit widens as the intensity diminishes. 
Again: the central power is indicated by the fact, that the 
first pair of legs is the strong pair; being properly hands, they 
contribute especially to the higher functions, that is, the support 
of the living animal, through their strength and powers of pre- 
hension, and not like the following, to locomotion. Thus, as 
we pass from the centre, the organs are of more and more hum- 
ble function. ( 
This centre, as we have observed in another place, is properly 
between the second antenns and mandibles. 'lhe second an- 
tennz and the rudimentary mouth, are among the first parts 
that appear in the embryo. If we look at it as a centre of force 
or of growth, we remark that the radii on opposite sides of this 
centre, before and behind, are very unequal, the latter being six 
or eight times as long as the former,—a relation which is the in- 
verse of the functional importance of the parts pertaining to each. 
Our idea of the condition of highest centralization is thus 
drawn from a study of the species. ; 
