Grouping together its several modes as above delineated, we see that { Unicentral { Central { or { Continuous { { Multicentral { or { { Discontinuous DEVELOPMENT is { or { { { Uniaxial { Axial { or { Continuous { Multiaxial { or { Discontinuous Any one well acquainted with the facts, may readily raise objections to this arrangement. He may name forms which do not obviously come under any of these heads. He may point to plants that are for a time multicentral but afterwards develop axially. And from lower types of animals he may choose many in which the continuous and discontinuous modes are both displayed. But, as already hinted, an arrangement free from such anomalies must be impossible, if the various kinds of organization have arisen by Evolution. The one above sketched out is to be regarded as a rough grouping of the facts, which helps us to a conception of them in their totality; and, so regarded, it will be of service when we come to treat of Individuality and Reproduction. § 51. From these most general external aspects of organic development, let us now turn to its internal and more special aspects. When treating of Evolution as a universal process of things, a rude outline of the course of structural changes in organisms was given (_First Principles_, §§ 110, 119, 132). Here it will be proper to describe these changes more fully.