ACTIVATION OF STARFISH EGGS BY BUTYRIC ACID. 



In Table I the figures represent the approximate percentages 

 of eggs forming free-swimming blastulse with each exposure. 

 The estimates of percentages were made in watch-glasses under a 

 low power; a large number of eggs were used in making each 

 estimate, collected at random from the bottom and sides of the 

 dish. The probable error of such estimates is assumed to be 

 about 5 per cent.; hence the values are given as approximations; 

 this procedure appears to be as accurate as the conditions permit. 

 There is always a clearly defined optimum in such a series; but 

 often two and sometimes three successive dishes near the optimal 

 region show equally good conditions, especially if the intervals 

 between successive exposures are brief. In such cases the opti- 

 mum used in calculating temperature coefficients is the arith- 

 metical mean of the favorable exposures. For convenience in 

 supervision the optima are printed in heavy type. 



Table II summarizes the results of the above experiments, and 

 gives the temperature-coefficients for each series. The coeffi- 

 cients are given as the ratios between the velocities at two 

 temperatures 10 part (<2io values), in accordance with the usage 

 customary in physiological literature. It is assumed that the 

 velocity increases through the entire interval of 10 at the same 

 proportional rate as through the observed interval of 2; the 

 value of <2io is then (T n /T n+2 } ', T n and r n+2 being the observed 

 optimal times of exposure at the two temperatures. 1 Each 

 value of Qio is derived from observations made upon the same 

 lot of eggs at the two temperatures. 



In each group the temperature-coefficient is seen to increase 

 steadily as the temperature rises. The two groups are best 

 compared if the Qw values are placed side by side as in Table III. 



Further experimental data are given in Table IV at the end of 

 the paper, which summarizes the results of all of last season's 

 experiments. In this table the experiments for each temperature 

 are grouped together; the decrease in the effective times of ex- 



1 The temperature-coefficient as thus expressed is obtained from any pair of 

 observations by the formula, 



10 



/ Vti\tl-t 



" \VtJ 



Vt l and Vt 2 being the velocities observed at the two temperatures ti and tz. 



