No. 3.] 



/:-.\7v-;AVj//-:.\v.s- /.\- 



MICE. 



123 



plant breeders "the type is broken." Plant breeders (e.g., 

 Focke and de Vries) have long ago observed that the progeny 

 of hybrids is extraordinarily variable. 



Fourth Generation. - - Several pairs of the foregoing descend- 

 ants of the reverted gray mice were mated, and thirty-one 

 young sorted into eight classes were obtained, as follows : 



As in the third generation, there is here great variation. 

 The results may be generalized as follows : 



(1) All descendants of albinic parents are albinos. 



(2) When both parents are gray and spotted all descendants 

 (2) are gray and spotted. 



(3) Gray 9 :: white $ gives 88 per cent gray and 12 per 

 cent walzers ; the white is shut out. 



(4) Gray 9 white walzer $ gives 44 per cent gray, 44 

 per cent walzers, and i 2 per cent white. 



Fifth Generation.- -To save room we will henceforth make 

 use of abbreviations for the names of colors, as follows : 



