CERTAIN LAWS OF VARIATION. 



191 



To determine the effect of temperature acting at the 

 time of impregnation, portions of the ova and sperma- 

 tozoa were shaken from the ovaries and testes in small 

 beakers of sea-water. After bringing these to the re- 

 quired abnormal temperature, their contents were 

 mixed, and the mixed solution kept at the same tempera- 

 ture for, in most cases, an hour. It was then poured 

 into a jar holding 2 to 4 litres of sea-water at the normal 

 temperature. The ova, now fertilised, were allowed to 

 develop under as constant conditions as possible for 8 

 days, and the larvae were then killed and measured in 

 groups of 50, as already mentioned. Other ova, kept 

 at the time of impregnation at a normal instead of an 

 abnormal temperature, were allowed to develop under 

 otherwise exactly similar conditions, and so afforded 

 " control " or " normal " larvae, against which the effect 

 produced in the other larvae by exposure to the abnor- 

 mal temperature could be determined. In the accom- 

 panying table the results obtained in the various obser- 

 vations are collected: * 



Here we see that exposure for an hour to a tempera- 

 ture of about 8 C. at the time of impregnation, instead 



* Vide Phil. Trans. 1895, B. p. 582, and Proc. Roy. Soc., vol. xlvii. 

 p. 85, 1900. 



