by hydrolysis or some other action of the increasing temperature. This latter is noticeable near the upper temperature limit. The reason that 1 and 3 interfere more strongly in life phenomena than in the chemical reactions of crystalloid substances may possibly be accounted for by the fact that the enzymes and most of the constituents of living matter are colloidal, _i. e._, consist of particles of a considerably greater order of magnitude than the molecules of crystalloids.[251] [249] A full discussion of the literature on temperature coefficients is given in A. Kanitz’s book on _Temperatur and Lebensvorgänge_, Berlin, 1915. [250] Van Slyke, D. D., and Cullen, G. E., _Jour. Biol. Chem._, 1914, xix., 141. [251] These considerations may meet the objections of Krogh to the application of the van’t Hoff rule of temperature effect on reaction velocity to life phenomena. See also the discussion of this subject in Kanitz’s book. We will now show the rôle of the temperature coefficient upon phenomena of development. F. R. Lillie and Knowlton[252] first determined the influence of temperature upon the development of the egg of the frog and showed that it was of the same nature as that of a chemical reaction. These experiments were repeated a year later by O. Hertwig.[253] [252] Lillie, F. R., and Knowlton, E. P., _Zoöl. Bull._, 1897, i. [253] Hertwig, O., _Arch. mikrosk. Anat._, 1898, li., 319. See also E. Cohen, _Vorträge für Aerste über physikalische Chemie._ 2d ed. Leipzig, 1907. The time required for the eggs to reach definite stages was measured for different temperatures and it was found that the temperature coefficient Q₁₀ between 2.5° and 6° was equal to 10 or more; between 6° and 15° it was between 2.6 and 4.5; between 10° and 20° it was 2.9 to 3.3, and between 20° and 24° it was between 1.4 and 2.0. To anybody who has worked on this problem it is obvious that no exact figures can be obtained in this way, since the point when a certain stage of development is reached is not so sharply defined as to exclude a certain latitude of arbitrariness. The writer found that very exact figures can be obtained on the influence of temperature upon development of the sea-urchin egg by measuring the time from insemination to the first cell division. Such experiments were carried out in a cold-water form _Strongylocentrotus purpuratus_ and a form living in warmer water, _Arbacia_.[254] The figures on _Arbacia_ have been verified by different observers in different years. [254] Loeb, J., _Arch. f. d. ges. Physiol._, 1908, cxxiv., 411; Loeb J., and Wasteneys, H., _Biochem. Ztschr._, 1911, xxxvi., 345; Loeb J., and Chamberlain, M. M., _Jour. Exper. Zoöl._, 1915, xix., 559. TABLE X INFLUENCE OF TEMPERATURE UPON THE TIME (IN MINUTES) REQUIRED FROM INSEMINATION TO THE FIRST CELL DIVISION