Laws of Incubation and Gestation. 



271 



(luring an unavoidable absence. I give the table herewitli, without 

 any attempt at compensating for errors. The law which they 

 clearly indicate is that 



where / is the time of hatching, T is the temperature at which 

 the eggs are kept ; ;;/ and a are constants, the latter being of 

 course the fixed temperature referred to. The last column gives, 

 the time (in hours) which the eggs would have taken to hatch 

 according to this law, assuming ;// = 40,200; and ff = l*3° C. for 

 this species. 



Table I. 



No. 6 is the set already referred to as having been marred by 

 an accident ; but the general agreement of the figures can leave 

 no doubt as to the accuracy of the law. 



In the formula given it is plain that a temperature of - l-3° C 

 would be that at which the eggs would take an intinite time to 

 hatch, or, in other words, would never hatch at all ; but at 

 temperatures somewhat above this we may be sure that other 

 circumstances would interfere to prevent the development of the 

 tadpole. 



The quantity m is constant only for a given species ; but in 

 what follows of this paper, enough will be seen to make it 

 probable that in comparing species with species, it is a quantity 

 varying directly as the sixth root of the weight of the fully 

 matured animal. 8o far as I can depend on the very few and 

 very rough observations made as to the hatching time of lizards. 



