112 



SCIENCE. 



[N. S. Vol. XIX. No. 472. 



house mouse, but of a ligliter color. Probably 

 the earlier crosses of Crampe (1877, p. 390, 

 391) with white and gray rats that led him to 

 the conclusion that in inheritance the color 

 of the species shuts out the color of the variety 

 were made with pure bred rats. Cuenot cross- 

 ing grays and albinos got gray mice without 

 exception in the F^ generation. 



From the foregoing the conclusion may be 

 drawn that the offspring of pure-bred gray 

 mice crossed with albinos inherit chiefly from 

 the wild form but that the color is slightly 

 modified, particularly when the albinos are not 

 pure bred, first by an increase in the yellow 

 and, secondly, in some cases, by the presence 

 of white. Gray is dominant over albinism but 

 the soma derived from hybrid germ cells shows 

 traces of the albinic blood. The dominance 

 is incomplete. The dominance, so far as it 

 goes, accords with De Vries's (1902, p. 145) 

 generalization that the older type or the wild 

 species is dominant over a more recent type 

 or a cultivated variety. 



When these gray mice are crossed inter se 

 there result gray mice and white mice in the 

 proportion of three to one (Cuenot; Castle 

 and Allen, 1903), and the albinos show them- 

 selves purely recessive. That all recessive 

 mice are, however, not alike, but differ accord- 

 ing to their ancestry has been argued by 

 Darbishire from the fact that pure bred al- 

 binos transmit less to F^ than albinos do that 

 are derived from a mixed ancestry. 



II. Wild Gray U5) X Black (9).— Two off- 

 spring of this cross were essentially of the 

 wild, maternal color. 



III. Wild Gray (29<S) X Chocolate ^21 | ). 



— Nos. 52 and 54 were marked like the wild 

 gray but were darker. No. 53 had a dark back, 

 a light yellow belly and white on the shoulders 

 and in the middle of the right flank. No. 55 

 had a back like the house mouse, but its 

 shoulders were white and its belly yellow and 

 white. In these offspring there was an at- 

 tempt at least at blending and there was a 

 cropping out of an ancestral white, but on the 

 whole the gray dominated. 



IV. BlacTcXAlUno.- 

 twice. 



-This cross was made 



1. Black 



/ r 2, black \ 

 r^ [9, black/ 



X albino { 18 I ' 



albino \ 

 albino / ' 



Five young were obtained, all reversions, be- 

 ing of typical wild laouse color except that 

 two of them had white spots on the belly. 



2. Black (126) X Albino 



f 35, yellow (6, albino X 



102 



57, reversion 



18, albino 



7, yellow) 

 7, yellow 



4, albino. 



5, albino 



— The two offspring were reversions, but one 

 had a white spot at the center of the belly. 

 These two matings indicate that neither black 

 nor white is dominant, but that the repressed 

 ancestral gray character is, as it were, liber- 

 ated. 



V. Black (137) X Yellow 



r 102, albino 



136 -i f 102, albino 



130, reversion -^ ^„„ ,, , 

 [ \ 126, black 



— The single offspring was a typical reversion 

 except that the front part of the belly and the 

 flanks were white. Bateson (1903, p. 85) 

 states that Miss Durham got sables and dingy 

 fawns and even blacks from this cross. In 

 any case there is no evident dominance. 

 The following cases are still more complex. 



white \ 

 yellow / 



VI. Bever 



>-sionl 32 -^ ^ 



X Gray I 



15, wild \ 

 5, white 7 " 



— There were two of the progeny of this pair 

 that survived infancy — both were of the 

 typical wild mouse color. 



(35, yellow 

 [57, gray j 7^ y^How 

 VII. Reversion- im\ 



. l'»- -"•{5: S 



