[D] This assertion is a direct corollary from the structure of the determinants and the idioplasm. If the idioplasm of the fertilizing cell were to pass through the membrane about the ovum by osmosis, its organized structure would be lost.--_Trans._ In the idioplasm of a germ cell arising from the crossing of unlike individuals the micellar rows of the individual determinants have sometimes an intermediate constitution and produce characteristics in the organism which are intermediate between the characteristics of the parents. Sometimes the micellar rows derived from the father and mother respectively lie side by side unchanged in the idioplasm of the offspring in distinct groupings and may reproduce in the organism their respective characteristics side by side, or only one of them may develop, while the other remains latent. On account of the union of both idioplasms as the result of fecundation, two sexually mature organisms are the more able to form with each other a viable germ cell, the nearer they are genetically related--that is, the more nearly the male and female idioplasms correspond in their configuration and chemical nature, because in this case the micellar arrangements are best suited to each other, and the idioplasm of the new fertile germ cell receives its most suitable nourishment from the mother. If, however, self-fecundation or the closest in-and-in breeding often yields products of less virility and is avoided by nature, this is the result of injurious influences which make themselves felt later on. This is because incompatibilities may be present in too closely related idioplasms and these are sources of weakness in unrestricted development. The more complicated is the idioplasm, the oftener this occurs, whereas absolute lack of crossing is not detrimental to the simplest (asexual) organisms. 11. ACTION OF EXTERNAL INFLUENCES.[E] The environment provides the organism above all with force and matter for its life processes. It causes no permanent variation and has only an ontogenetic significance, if the limits of the idioplasmic elasticity are not exceeded; it maintains the growth and metabolic assimilation of the individual, and conditions individual (not hereditary) differences, which constitute "nutrition varieties." (See page 30.) These appear as the direct results of operating causes.