Certain Laws of Variation. 



95 



kept at about 20', and the abnormal ones were kept for varying num- 

 bers of hours at about 8, whereby a negative effect on growth was 

 produced. In another, the normal larvae were kept at 13, the 

 abnormal at 22', a positive effect being produced, and in the third the 

 normal larvae were kept at about 24- and the abnormal ones for varying 

 periods at about 26 \ whereby a negative effect, followed by a positive 

 one, was produced. 



The results are arranged in this table according to the times duiing 

 which the larvae were exposed to abnormal conditions. The means of 

 these times are also given, as comparisons are thereby rendered easier. 

 In the first line of the left portion of the table is given the average 

 effect produced in the ten experiments already quoted, in which the ova 

 were kept at about 8 at the time of impregnation. (The experiments 

 in which the time of exposure was one to three minutes have been 

 omitted, as the effect produced in this case was probably something 

 special, directly connected with the act of impregnation.) The results 

 in this group of observations show a fairly regular and very rapid 

 diminution in the effect produced on the size of the larvae with pro- 

 gress in development, but unfortunately they extend only to the 21st 

 jhour. The results in the middle portion of the table extend to the 

 192nd hour, but they are very irregular. Nevertheless they also, on 

 "the whole, show a rapidly diminishing effect. The results in the right 

 portion of the table bear out this result more fully. In the first line is 

 given the mean of the seven observations in which the ova were kept 

 at 26 at the time of impregnation. In the next three observations in 

 the table, in which the mean time of exposure was 2 '5 hours, the mean 

 effect produced was 4*1 per cent. In the 10th hour it was 1*4 per 

 cent., in the 15th to 17th hours on an average 0'36 per cent., and in 

 the 83rd hour on an average only O008 per cent. All the observations 

 made, therefore, whether taken in the small groups in which they were 



