Castle has long stoutly maintained the effect of such selection, and his forces have recently been augmented by Jennings. The experimental work now in process will doubtless yield a decisive answer.
Conclusion.
A comparison of the simple descriptive natural history of a century ago with the foregoing manifold developments of modern biology will indicate the wonderful progress which has occurred during this period. The path has led from the crude methods of the almost unaided eye and hand to the applications of the most delicate experimental apparatus. For the marvelous success which zoology has attained has been possible only by the skillful use of scalpel, microscope, microtome and other mechanical devices and by the refined methods of the chemist and physicist.
The central truth to which all these discoveries consistently point is the unity and harmony of all biological phenomena, and indeed of all nature. No longer does the zoologist find any demarcated line separating his field of research from that of the botanist or the chemist or even of the physicist, for all the natural sciences obviously deal with closely associated phenomena. The aim of the future will be both to complete fields of study already marked out and to derive a comprehensive explanation of the general principles involved.
Notes.
[172]. Proc. Biol. Soc. Washington, 3, 35, 1886.
[173]. Ibid., 4, 9, 1888. Both of these papers are reprinted in Ann. Rept. Smithsonian Inst., 1897, U. S. Nat. Mus., Pt. 2, pp. 357–466, 1901.
[174]. Louis Agassiz: his Life and Correspondence, by Elizabeth Carey Agassiz, p. 145, 1885.
[175]. List of North American Land Mammals in the United States National Museum, 1911. Bull. 79, U. S. Nat. Mus., 1912.
[176]. Birds of North and Middle America, Bull. 50, parts I-VII, U. S. Nat. Mus., 1901–1916.