The assumption that atrophy and reduction are the inevitable consequence of disuse, or diminution of use, in so far as this decreases the flow of nourishing blood to unexercised parts, is certainly erroneous. Yet Darwin made it the premise of his argument from so-called rudimentary organs. “The term ‘disuse’ does not relate,” he informs us, “merely to lessened action of muscles, but includes a diminished flow of blood to the part or organ, from being subjected to fewer alternations of pressure, or from being in any way less habitually active.” (“Origin of Species,” 6th ed., p. 469.) As a matter of fact, however, we have many instances in which use has failed to develop and disuse to reduce organs in certain types of animals. As an example in point, we may cite the case of right-handedness among human beings. From time immemorial, the generality of mankind have consistently used the right hand in preference to the left, without any atrophy or reduction of the left hand, or over-development of the right hand, resulting from this racial practice. “The superiority of one hand,” says G. Elliot Smith, “is as old as mankind.” (Smithson. Inst. Rpt. for 1912, p. 570.) It is true that only about 6,000 years of human existence are known to history, but, if one accepts the most conservative estimates of glaciologists, man has had a much longer prehistory, the lowest estimates for the age of man being approximately 30,000 years. Thus W. J. Sollas tells us that the Glacial period, in which man first appeared, came to an end about 7,000 years ago, and that the men buried at Chapelle-aux-Saints in France lived about 25,000 years ago. His figures agree with those of C. F. Wright, who bases his calculations on the Niagara Gorge. The Niagara River is one of the postglacial streams, and the time required to cut its gorge has been calculated as 7,000 years. Gerard De Geer, the Swedish scientist, gives 20,000 years ago as the end of glacial and the commencement of recent or postglacial time. He bases his estimates on the sediments of the Yoldia Sea in Sweden. His method consists in the actual counting of certain seasonally-laminated clay layers, presumably left behind by the receding ice sheet of the continental glacier. The melting is registered by annual deposition, in which the thinner layers of finer sand from the winter flows alternate with thicker layers of coarser material from the summer flows. In warm years, the layers are thicker, in colder years they are thinner, so that these laminated Pleistocene clays constitute a thermographic as well as a chronological record. De Geer began his study of Pleistocene clays in 1878, and in 1920 he led an expedition to the United States, for the purpose of extending his researches. (Cf. _Science_, Sept. 24, 1920, pp. 284-286.) At that time, he claimed to have worked out the chronology of the past 12,000 years. His figure of 20,000 years for postglacial time, while very displeasing