So far, then, we have testimony to this point, as it were, from a reluctant witness. But if we have no theory involving the "stability of germ-plasm" to maintain, we can scarcely fail to see how susceptible the germ-plasm is likely to prove to changed conditions of life. For we know how eminently susceptible it is in this respect when gauged by the practical test of fertility; and as this is but an expression of its extraordinarily complex character, it would indeed be surprising if it were to enjoy any immunity against modification by changed conditions of life. We have seen in the foregoing chapter how frequently and how considerably somatogenetic changes are thus caused, so as to produce "somatogenetic species"--or, where we happen to know that the changes are not hereditary, "climatic varieties." But the constitution of germ-plasm is much more complex than that of any of the structures which are developed therefrom. Consequently, the only wonder is that hitherto experimentalists have not been more successful in producing "blastogenetic species" by artificial changes of environment. Or, as Ray Lankester has well stated this consideration, "It is not difficult to suggest possible ways in which the changed conditions, shown to be important by Darwin, could act through the parental body upon the nuclear matter of the egg-cell and sperm-cell, with its immensely complex and therefore unstable constitution.... The wonder is, not that [blastogenetic] variation occurs, but that it is not excessive and monstrous in every product of fertilization[124]." [124] _Nature_, Dec. 12, 1889, p. 129. If to this it should be objected that, as a matter of fact, experimentalists have not been nearly so successful in producing congenital modifications of type by changed conditions of life as they have been in thus producing merely somatic modifications; or if it should be further objected that we have no evidence at all in nature of a "blastogenetic species" having been formed by means of climatic influences alone,--if these objections were to be raised, they would admit of the following answer.