creative divinity, and afterward to the individual and to the species or race, or, in a manner equally exclusive, to the environment. The logic in this connection recalls the best days of the scholastic with his distinctions between the causa efficiens, first causes, second, final, real, formal, etc.
According to Weismann :
If a phenomenon is produced only under certain conditions, it does not therefore follow that the conditions are also the cause of the phenomenon. The warmth of the setting hen is a condition without which the young chick cannot be developed, but we should have difficulty in maintaining that it is to the heat that the eggs of the hen are indebted for the faculty of becoming chickens. This faculty is evidently altogether the outcome of an infinitely long phyletic development, finally terminating in a physico-chemical structure of the egg and spermatic cell, so that from their union the result must be a chicken, and not a goose or duck, on the supposition of the accomplishment of certain conditions required by this individual—conditions of development among which heat also figures. In a word, it is therefore the physical nature of the egg that is the cause of the development of the chicken.
Weismann gives still other examples, in support of the conclusions of his formal logic. An ivy branch may be inverted in such a way that the root exposed to the light will produce leaves, and that the old part of the leaves will produce roots. According to him, this double adaptation has for cause, not the influence of the external causes in connection with the nature of the ivy, but the peculiar nature of the latter.
If the tree frog changes in color—if it is pure green while it lives upon green leaves, and from brown to black when placed in a somber environment—this change of color depends upon a very complicated reflex mechanism. In fact, the modifications of the coloring cells of the skin are not due to differences in the illumination upon the skin through the light, for the reason that blind frogs do not react from the changing illuminations of the environment. There is, according to him, but one possible explanation—that of the process of natural selection according "to the differences in the reaction of the organism in possession of itself But how can a reflex action be explained without the outside stimulation ? Here is, indeed, the revival of the indi-
