And while these forms of variation may be the special prerogative of the male, we may perhaps see, in superabundant female vigour, a not less important source of developmental and embryonic variations in the offspring. The characteristic selfishness of the male applies his surplus vitality to the adornment of his own person; the characteristic self-sacrifice of the mother applies her surplus vitality to the good of her child. Here we may have the source and origin of those variations in the direction of fosterage and protection which we have seen to have such important and far-reaching consequences in the development of organic life. The storage of yolk in the ovum, the incubation of heavily yolked eggs, the self-sacrificing development in the womb, the elaboration of a supply of food-milk,--all these and other forms of fosterage may well have been the outcome of superabundant female vigour, the advantages of which are thus conferred upon the offspring. We may now proceed to note, always remembering the paramount importance of the organism, some of the effects produced by changes in the environment. The most striking and noteworthy feature about the effects of changes of climate and moisture, changes of salinity of the water in aquatic organisms, and changes of food-stuff, is that, when they produce any effect at all, they give rise to _definite_ variations. Only one or two examples of each can here be cited. Mr. Merrifield,[EK] experimenting with moths (_Selenia illunaria_ and _S. illustraria_), finds that the variations of temperature to which the pupa, and apparently also the larva, are subjected tend to produce "very striking differences in the moths." On the whole, cold "has a tendency, operating possibly by retardation, to produce or develop a darker hue in the perfect insect; if so, it may, perhaps, throw some light on the mechanism so often remarked in north-country examples of widely distributed moths." Mr. Cockerell[EL] regards moisture as the determining condition of a certain phase of melanism, especially among Lepidoptera. The same author states that the snail "_Helix nemoralis_ was introduced from Europe into Lexington, Virginia, a few years ago. Under the new conditions it varied more than I have ever known it to do elsewhere, and up to the present date (1890) 125 varieties have been discovered there. Of these, no less than 67 are new, and unknown in Europe, the native country of the species." The effects of the salinity of the water on the brine-shrimp _Artemia_ have already been mentioned. One species with certain characteristics was transformed into another species with other characteristics by gradually altering the saltness of the water. So, too, in the matter of food, the effects of feeding the caterpillars of a Texan species of _Saturnia_ on a new food-plant were so marked that the moths which emerged were reckoned by entomologists as a new species.