16 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 oc- 

 cupy more room than the first pair of legs. The organs are all 

 small, the antennae exceedingly short, the maxillae small lamellar 

 organs sparingly jointed. The vegetative powers of growth 

 have had but little play. The inner antennas 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 maxillae (or outer maxillipeds) cover exactly the other 

 pairs, and shut closely down over the mouth, like a well-fitting 

 operculum to the buccal area. 



We hence learn, that the condition of highest centralization 

 in Crustacea, is where the cephalic part embraces the largest 

 portion of the normal structure of the cephalothorax, and the 

 whole is contracted within the smallest compass, with the least 

 vegetative growth 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 antennae; 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, is 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 antennae and mandibles. The second an- 

 tennae 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. 



