Certain Laws of Variation. 



87 



Larvae impregnated for an hour at about 11 were, on an average, 

 4'0 per cent, smaller than the normal, or practically the same as in the 

 case of Stroii yylocentrot us larvae. An abnormally high temperature does 

 not seem so effective, however, judging from the few results available. 

 Thus one hour's expostire to about 27 caused only 1*7 per cent, diminu- 

 tion, and five minutes' exposure 2 -6 per cent. It should be mentioned 

 that both in this case and that of Strongylocentrotus, the conditions of 

 the short-time exposure experiments differed in one respect from the 

 others, as the beakers of abnormally cooled or warmed ova were poured 

 directly into jars of water at normal temperature, and were not first 

 gradually warmed or cooled. That the shock of this sudden change of 

 temperature cannot be held accountable for much of the effect produced, 

 is proved by the fact that in those experiments in which the time of 

 exposure was reduced to ten seconds, only 1*7 per cent, diminution in 

 the size of the larvae was produced altogether. 



Experiments were now made to determine the effect of exposure to 

 abnormal temperatures during later stages of development. In each 

 case all the ova were kept for the first hour during impregnation at the 

 same temperature, and were then divided up into two portions, which 

 were poured into jars of water at different temperatures. In the first 

 experiment, made in March, the temperature of the Aquarium tank 

 water was on an average 12 '9, or distinctly low. Some of the ova, 

 after an hour's impregnation at 13'2, were accordingly poured into a 

 jar of water kept at 22. At various later periods the contents of this 

 jar were stirred up, and portions of it poured into smaller jars, which 

 were then transferred to the tank of running water at 12 '9. The 

 temperature of 22, which previous experiments had shown to be about 

 the most favourable for the development of the larvae, was maintained 

 practically constant by keeping the jar in a larger vessel of water, 

 which in its turn rested on the top of a water-bath warmed very 

 slightly by means of a gas flame provided with a regulator. The 

 results obtained in this experiment are given in the following table, 

 the body length of the normal larvae, or those kept at 12 '9 during the 

 whole of their development, being taken as 100 : 



For some unaccountable reason, the larvae developing from ova kept 



H 2 



