134 RALPH S. LILLIE. 



beakers, each containing a thermometer; after the eggs had 

 settled the sea- water was removed as far as possible; then the 

 solutions of butyric acid, at the temperatures chosen for the 

 experiment, were added, first to one beaker, and then, after a 

 short definite interval (e. g., 10 seconds), to the second. The 

 temperature of each beaker was kept constant during the period 

 of the experiment by immersion in* a water-bath of the same tem- 

 perature; and at definite intervals eggs were transferred to finger- 

 bowls containing sea-water. A series of dishes, each containing 

 eggs exposed to .006 n butyric acid for a definite length of time 

 (e. g., i m., 2 m., 3 m., etc.), was thus obtained for each temper- 

 ature. The intervals between successive transfers varied from 

 \ min. at the higher temperatures (22 and over) to 3 or 4 minutes 

 at 8 to 12. The condition of the eggs in each dish and the 

 proportion developing to larval stages were determined later. 

 The differences between successive members of such a series are 

 usually distinct, and the proportion of favorably developing 

 eggs is always found to increase progressively up to an optimum, 

 after which it declines. The determination of the optimum dura- 

 tion of exposure thus presents no difficulties. As a rule one dish 

 shows distinctly more numerous larvae than those on either side; 

 but with favorable lots of eggs and brief intervals between the 

 transfers it is often found that at the region of optimum two or 

 even three successive exposures give equally good results. 



At temperatures below 8 it is necessary to distinguish between 

 the effects due to the butyric acid, and those produced directly 

 by cold alone. Prolonged exposure to temperatures of 6 and 

 lower has a well-marked activating influence on star-fish eggs. 1 

 At these temperatures butyric acid solutions were found to act 

 more rapidly than at temperatures several degrees higher (8 to 

 12) ; this increase in the rate of activation with fall of temperature 

 indicates the entrance of cold as a factor; we have then to deal 

 with a summation of two activating influences, cold and acid. 

 Between 8 and 28 the influence of temperature alone is insuf- 

 ficient for activation. Above this range temperature conditions 

 again become effective; simple exposure to sea-water at 30 and 

 higher for the proper length of time complete activation. 2 There 



1 Cf. Greeley, Amer. Journ. Physiol., 1902, Vol. 6, p. 296. 



2 R. S. Lillie, BIOLOGICAL BULLETIN, loc. cit. 



