The compactness of the class Crustacea is generally admitted; of the precise affinities of its subdivisions there is still much to learn.
The expression is usually written, for compactness, a+ b + c + d + & c. The numbers a, b, c, d,..
The aporose corals, too, have a practically identical structure, their compactness being due to the union of the trabeculae throughout their entire lengths instead of at intervals, as in the Perforata.
For the sake of compactness and convenience of reading the extension of the springs, and consequently the load, is frequently indicated on a dial, by means of a small rack and pinion, which give motion to a finger on the dial-plate, but the regularity and correctness of the indications of the finger will depend upon the condition of the rackwork and upon the friction, and these will vary with the wear of the machine.
Tillage operations on such land are easily interrupted by rain, and the period always much limited in which they can be prosecuted at all; the compactness and toughness of the soil renders each operation more arduous, and its repetition more necessary than in the case of dry land.