252 THE SCIENTIFIC MONTHLY
commonly oymn and sperm, which^ leading a life aloof from the body cellfl, give rise to the new individual.
We may then ask, do all individual differences that are heritable originate from the very start in the germ cells, and, if so, owing to what influences? or are there subtle changes of the body cells induced by habit, food and environment, which are transmitted to and lodged in some potential form, in the germ cells? This two-sided question, it is obvious, concerns mankind in a very practical way. It has been argued warmly for many years, usually under the heading of ^^ the inheritance of acquired characters,'^ and still to-day, in a more clearly circumscribed shape than formerly, makes one of the most important general problems of experimental biology.
In past years it was widely held that the transmission from body to germ was a fact, in other words, that peculiarities developing for fhe first time in the body, not as the residt of congenital constitution, but as the result of habit or outward circumstance, were transmissible to the germ. Weismann and others have shown that much of the evidence on which this conclusion rested is weak, and the result of their criticism has been in some measure to discredit the idea. There are, nevertheless, certain experiments which, while not demonstrating transmission from body to germ, do demonstrate perhaps the more important fact that the effect on the body of outward circumstance in one generation may be in some degree repeated in the bodies of the next generation, although the conditions which first induced the change are no longer operative.
Prominent among such experiments are the classic investigations of Standfuss and Fischer on European butterflies. Both Standfuss and Fischer showed for certain species that the temperature at which the pupal stage is kept, during its so-called sleep, may be made to affect very seriously the coloration of the butterfly into which it metamorphoses. In this way by emplo}ring temperatures above the normal and tempera- tures below the normal, butterflies are obtained very different in appear- ance from the type.
Standfuss having in this way obtained strongly altered individuals, bred from them, keeping the butterflies and their offspring not at the abnormal temperature which induced the change, but at the normal tem- perature. The great bulk of the offspring, the second generation of butterflies, proved to adhere to the usual type of the species. Never- theless, a few examples departed from the type and resembled in varying degrees their parents.
In a similar experiment, Fischer subjected pupse to an intermittent cold of — 8"* C, and in this way obtained butterflies different from the type. The offspring of these modified individuals fell into two groups, those adhering to the type and those resembling in greater or less degree the modified parents. The percentage of the latter was a consider- able one.
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