For a proper understanding of this, it must be realized that it is impossible for bodies organized in a thousand ways in relation to particular ends to be constructed by the general laws of the communication of motion, which depend on this law, that every body is moved in proportion to the force impelling it, and in the direction in which the force impels it, and that the entire utility to be drawn from these laws with respect to organized bodies is to develop and enlarge the parts of which the embryos or seeds of animals or plants are composed.