1398 CRUSTACEA. 



sensorial function. The perfection 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 abdomen, in the 

 .first place, is reduced to its minimum size. Vegetative 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 con- 

 centration ; and we find that the limit widens as the intensity dimi- 

 nishes. 



Again : the central power is indicated by the fact, that the first pair 

 of legs is the strong pair ; being properly hands, they contribute espe- 

 cially to the higher functions, that is, the support of the living animal, 

 through their strength and powers of prehension, and not like the 

 following, to locomotion. Thus, as we pass from the centre, the organs 

 are of more and more humble function. 



This centre, as we have observed in another place, is properly between 

 the second antennae and mandibles. The second antennae 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 en 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 inverse 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. 



The most perfect state of it is seen in the Maia group, in which the 

 bases of the antennae and eyes are crowded into the narrowest possible 

 compass, and the mouth organs are well compacted within the buccal 

 area, and the legs and whole system have the highest completeness. 



The form of the body of a Maia is a somewhat flattened ovoid, nar- 

 rowest in front; and the middle point between the mouth and the 

 second antennae^ which we call the potential centre of the animal, is 

 situated near the front, say about half an inch from the front outline 

 (excluding the beak), supposing the cephalothorax three inches long. 

 We may call the part anterior to this centre, A; the part posterior, 

 B; and the length of the former, measured on the axis, a; of the 

 latter, b. These parts may be viewed, as regards development, as 



