Milne-Edwards frankly takes up the teleological standpoint, and interprets organic forms on the assumption that they are purposive and rationally constructed. "To arrive at an understanding of the harmony of the organic creation," he writes, "it seemed to me that it would be well to accept the hypothesis that Nature has gone about her work as we would do ourselves according to the light of our own intelligence, if it were given us to produce a similar result. Comparing and studying living things as if they were machines created by the industry of man, I have tried to grasp the manner in which they might have been invented, and the principles whose application would have led to the production of such an assemblage of diversified instruments" (p. 435). The problem is to discover the laws which rule the diversity of organic forms. The first and most obvious of these laws is the "law of economy," or the law of unity of type. Nature, as Cuvier pointed out, has not had recourse to all the possible forms and combinations of organs; she appears to work with a limited number of types and to get the greatest possible diversity out of these by varying the proportions of the constitutive materials of structure. Within the limits of each type Nature has brought about diversity by raising her creatures to different degrees of perfection. This is the second law of organic form, and it is this law that Milne-Edwards chiefly elaborates. Degrees of perfection mean for him, as for Aristotle, primarily degrees of perfection of function, but since structure is necessarily in close relation with function, perfection of function brings in its train increased perfection of organisation. This can only be attained by a division of labour[306] among the organs and by their consequent differentiation. An animal is like a workshop where some complicated product is manufactured, and the organs are like the workmen. Each workman has his own special piece of work to do, at which he becomes thoroughly expert; and the finished product is manufactured more rapidly and efficiently by the co-operation of workers each skilled in one department than it would be if each workman had to produce the whole. Applied to the organism this principle of the division of labour means the differentiating out of the separate functions, their localisation in different parts of the organism, and their co-ordination to produce a combined result.