Laics of Variation. '.)! 



influence of the later hours was only very partially able to counteract 

 it. Thus, during the 1st to 4th hours, the diminution effected was no 

 less than 6 -45 per cent, per horn-. There was even a slight additional 

 diminution during the next 3-1- hours, but after that the increase in size 

 noticed in the above experiment set in. It is probable that an un- 

 favourable effect persisted even to the first portion of the 7 to 11 hour 



period, as the percentage increase per hour is considerably less than one 

 would expect. The only values which are unequivocally genuine are, 

 therefore, the last two. From these we see that the effect produced 

 between the 22nd and 44th hours is only an eighth of that between the 

 llth and 22nd hours. 



It was thought that perhaps the very marked diminution produced in 

 the size of the larvae might be in part due to the rather sudden changes 

 of temperature to which the developing ova were subjected. These 

 changes were not, as a matter of fact, by any means remarkably sudden, 

 as the water in which the ova were placed after impregnation took 

 about fifteen minutes to attain its temperature of 26', whilst the reverse 

 change from 26 to 24-2, the temperature of the tank water in this 

 experiment, took about ten minutes. Still, to test this supposition, 

 some of the ova used in this experiment were subjected to several 

 changes of temper.ature. Thus, one portion, directly after the first 

 hour's impregnation, was kept three hours at 26', then seven hours at 

 24'2, then fourteen hours at 26, and the remainder of the time 

 at 24-2. The size of the larvae obtained therefrom was 85-89, or, 

 if anything, somewhat larger than one would have expected. Another 

 portion of the ova was kept for the 1st to 7|th hours at 24'2, the 7|th 

 to 22nd hours at 26'0 C> , and the remainder of the time at 24'2. The 

 size of these larvae was 94-93, or 5 per cent, less than the normal. One 

 would have expected them to be if anything slightly larger than the 

 normal, as they were kept at the lower and favourable temperature 

 during the first 6| hours. Still, these two experiments, taken together, 

 show that the effect of even several changes of temperature can only be 

 slight. 



