The similar responses to diverse stimuli or the similar results produced by diverse causes are the conditions which make an analysis and the isolation of causes necessary. With departures from the normal and optimum into zones of stimulation and of unfavorable conditions many similar effects or results are produced. The similar results of extremes of high and low temperature as shown in Fischer’s experiments on Lepidoptera, and the effects of high temperatures, aridity, and the lack of oxygen may be cited as examples. Such effects have an important bearing upon the subject of physical and chemical _limiting factors_ which influence individuals, aggregations, and associations. BLACKMAN, F. F. 1905. Optima and Limiting Factors. Ann. of Bot., Vol. XIX, pp. 281-295. “When a process is conditioned as to its rapidity by a number of separate factors, the rate of the process is limited by the pace of the ‘slowest’ factor.” p. 289. 1908. The Manifestations of the Principles of Chemical Mechanics in the Living Plant. British Assoc. Adv. Sci., 1908, pp. 1-18. ADAMS, CHAS. C. 1904. On the Analogy Between the Departure from Optimum Vital Conditions and Departure from Geographic Life Centers. Science, N. S., Vol. XIX, pp. 210-211. GREELEY, A. W. 1901. On the Analogy Between the Effects of Loss of Water and Lowering of Temperature. Amer. Jour. Physiol., Vol. VI, pp. 122-128. ZOETHOUT, W. D. 1899. On Some Analogies Between the Physiological Effects of High Temperature, Lack of Oxygen, and Certain Poisons. Amer. Jour. Physiol., Vol. II, pp. 220-242. LYON, E. P. 1902. Effects of Potassium Cyanide and of Lack of Oxygen upon the Fertilized Eggs and the Embryos of the Sea-Urchin (_Arbacia punctulata_). Amer. Jour. Physiol., Vol. VII, pp. 56-75. PACKARD, W. H. 1905. On Resistance to Lack of Oxygen and on a Method of Increasing this Resistance. Amer. Jour. Physiol., Vol. XV, pp. 30-41. 1907. The Effect of Carbohydrates on Resistance to Lack of Oxygen. Amer. Jour. Physiol., Vol. XVIII, pp. 164-180. FISCHER, E. 1903. Lepidopterologische Experimental-Forschungen. III. Allgem. Zeit. für Entomologie, Bd. VIII, pp. 221-228. These experiments illustrate in a very striking manner how abnormally high and low temperatures produce the same kind of effect or response. _2. A Selection of Physiological and Ecological Papers_ (Alphabetically arranged) CLESSIN, S. 1897. Über den Einfluss der Umgebung auf die Gehäuse der Schnecken. Württemberg naturw. Jahreshefte 53, pp. 68-86. COLTON, H. S. 1908. Some Effects of Environment on the Growth of Lymnaea columella Say. Proc. Acad. Nat. Sci. Phila., 1908, pp. 410-448. KELLER, C. 1887. Humusbildung und Bodenkultur unter dem Einfluss tierischer Thätigkeit. Not seen. KNAUTHE, K. 1898. Zur Kenntnis des Stoffwechsels der Fische. Archiv f. d. gesammte Physiol. (Pflüger), Bd. LXXIII, pp. 490-500. LANG, A.