24 Studies in the Theory of Descent. 



happens that out of a hundred cases there occuis 

 one in which a chrysalis of the winter gene- 

 ration, having been forced by warmth, under- 

 goes transformation before the commencement 

 of winter, and emerges in the summer form, 16 this 

 is not in the least inexplicable. It cannot be 

 atavism which determines the direction of the 

 development ; but we see from such a case that 

 the changes in the first two generations have 

 already produced a certain alteration in the third, 

 which manifests itself in single cases under favour- 

 able conditions (the influence of warmth) by the 

 assumption of the Prorsa form ; or, as it might be 

 otherwise expressed, the alternating heredity (of 

 which we shall speak further), which implies the 

 power of assuming the Prorsa form, remains latent 

 as a rule in the winter generation, but becomes 

 continuous in single individuals. 



It is true that we have as yet no kind of insight 

 into the nature of heredity, and this at once shows 

 the defectiveness of the foregoing explanation ; but 

 we nevertheless know many of its external phe- 

 nomena. We know for certain that one of these 

 consists in the fact that peculiarities of the father 

 do not appear in the son, but in the grandson, 

 or still further on, and that they may be thus 

 transmitted in a latent form. Let us imagine a 

 character so transmitted that it appears in the 

 first, third, and fifth generations, remaining latent 

 18 See Exp. 10, Appendix I. 



