CERTAIN LAWS OF VARIATION. 



195 



6.4 per cent, smaller than these, or were, on an average, 

 diminished in size 1.28 per cent, for each hour's expos- 

 ure. An exposure of the ova for a further four hours 

 produced only 1.24 per cent, more diminution in the 

 size of the larvae, or .31 per cent, per hour, whilst still 

 eleven hours more produced an additional 2.28 per cent, 

 diminution, or .21 per cent, per hour. Taking means of 

 the various hours of exposure, one can therefore say 

 that the effect produced during hour 3^ was 1.28 per 

 cent., or about four times greater than that produced 

 during hour 8, and six times greater than that in hour 

 15J. That is to say, the effect produced very rapidly 

 diminished with progress in development. 



Other observations were made at a colder season of 

 the year, and in these the normal larvae were kept at 

 about 13, and the " abnormal " at about 22. An in- 

 crease in the size of the larvse was of course produced 

 thereby, and here again the effect was very much 

 greater for exposure during the earlier hours of devel- 



