192 CERTAIN LAWS OF VARIATION. 



of one of 19 C., produced, in ten observations, an aver- 

 age diminution of 4.1 per cent, in the size of the larvae. 

 Temperatures a few degrees above the normal acted 

 even more unfavourably, one of 25.5 producing, in 

 seven observations, an average diminution of 5.9 per 

 cent. It follows, therefore, that at the time of their 

 impregnation, the ova are most extraordinarily sensi- 

 tive to the temperature of their surroundings, be it ab- 

 normally high or abnormally low. Further observa- 

 tions showed that they were also very sensitive to an- 

 other condition, viz., salinity of the water, though not 

 to the same extent as to temperature. It seems very 

 probable, therefore, that at this period they are very 

 sensitive to all conditions of environment, whatever 

 their nature. 



The results contained in the lower half of the table 

 are even more remarkable than those in the upper. 

 Thus, if the ova were kept at about 8 or at 25.5 for 

 only one to three minutes after the mingling of the 

 solutions containing the ova and spermatozoa, and after 

 this short period were poured into jars of water at nor- 

 mal temperature, an average diminution in size of re- 

 spectively 3.3 and 5.1 per cent, was effected! The ob- 

 servations made are not very numerous or regular, and 

 hence not much importance can be attached to the actual 

 figures, but one is justified in concluding that the effect 

 produced is not so very much smaller than when the 

 period of exposure to the abnormal temperature <was an 

 hour. Now during a minute's time little more than the 

 impregnation of the ovum would be accomplished. 

 The processes connected with the fusion of the male 

 and female pronuclei and the commencement of seg- 



