194 CERTAIN LAWS OF VARIATION. 



these slighter effects it should be mentioned that this 

 organism throughout its growth was found to be dis- 

 tinctly less reactive to its environment than was 

 Strongylocentrotus. 



In order to determine the effect of exposure to ab- 

 normal temperatures during the later stages of devel- 

 opment, all the Strongylocentrotus ova were kept for 

 the first hour during impregnation at the same tempera- 

 ture, and were then divided up into two portions. One 

 portion was poured into a jar of water at a normal 

 temperature, and the larvae obtained therefrom used as 

 control larvae, whilst the other was poured into water 

 previously brought to an abnormal temperature. After 

 a few hours, the contents of this jar were vigorously 

 stirred, and some of them poured off into a smaller jar. 

 This was then transferred to the tank of running water 

 containing the control jar, and kept there during the 

 remainder of larval develpoment. A few hours later 

 another portion was withdrawn from the abnormal tem- 

 perature jar, and similarly treated. The kind of result 

 thereby obtained may be gathered from the following 

 table: 



SIZE. PER CENT. DIMINUTION IN DURING 



SIZE PER HOUR. 



Normal larvae (22. 5) , 100.0 



1-6 hrs. at 12, 93.61 1.28 1-6 hrs. 



1-10 hrs. " 92.37 .31 6-10 hrs. 



1-21 hrs. " 90.09 .21 10-21 hrs. 



Here the size of the " normal " larvae, grown through- 

 out at a temperature of 22.5, is taken as 100. 

 Larvae obtained from ova kept at a temperature of 

 about 12 from the end of the first hour after impreg- 

 nation to the end of the sixth hour were found to be 



