OO — 
EXPERIMENTS IN INHERITANCE. 173 
Durham did not carry any mating of the above type into the F, generation. 
Chocolate carrying silver-fawn (Dd bb) x silver-fawn (dd bb). 
F, 7 chocolate : 10 silver-fawn observed. 
8:5 8:5 calculated 1 . 1 ratio, 
Blue x_ silver-fawn. 
No matings dd BB x dd bb. But, as above recorded, a black carrying blue 
(Dd BB) x silver-fawn (dd bb) gave black and blue in F,. 
F, from these F, blues (dd Bb): 
2 blues : 2 silver-fawns. 
4 1 ex pair blues of unknown parentage. 
6 3 
46 17 Durham. 
52 20 observed. 
54 18 calculated 3. 1 ratio. 
Silver-fawn x silver-fawn. 
Silver-fawns should breed true, since they represent the lowest term of the epistatic 
colour series associated with absence of factor for dense deposition of pigment. 
Zygotic formula dd bb. 
Five matings between silver-fawns gave 28 silver-fawn young. 
APPENDIX A. 
Average Number of Young in Latter. 
Durham’s data are included for comparison; each of her averages 
is based on at least 75 litters. 
Average per litter 
Laurie Durham 
Yellow x yellow . . . . . . . +. 8:64 (81 litters) 3-90 
Yellow x other colour : 4 : é : . 474(54 ,, ) 3-97 
Agouti SChACOULINE SAM Aire svi xo) Hotel so) Poaet We. 3-47 
Agouti x other colour (not yellow). . .  . 3:32 
Black x<Gablack. jal ) «57 wruw ss teks 4:83 (23 ,, ) 4-60 
Black x other colour (not yellow) . 4:29 (14 ,, ) 3-99 
Blue <Vipliews 24) se ae, Pace 4:24(21 ,, ) 
Blue x other colour (not yellow) . 5-12 (26 ,, ) 
Chocolate x chocolate . . . . 4:32(25 ,, ) 3:96 
Chocolate x other colour (not yellow) . 4-71(34 ,, ) 3-93 
Silver-fawn x silver-ffawn . . . . 560(5 ,, ) 
Silver-fawn x other colour (not yellow) . 4:79 (14 ,, ) 
Albino x albino a ee 5-18 (17 ,,_ +) 
Albino x yollow. . «..-! 4:60(25 ,, ) 
Albino x colour (not yellow) 4:19 (41 ,, ) 4:27 
In the above records, both Miss Durham’s and my own, only 
those mice are counted which lived long enough for their colours’ to 
be determined. 
The strikingly smaller size in my experiments of the average litter 
ex yellow x yellow, as compared with the other matings, is commented 
on above. A lesser difference was observed by Cuénot also (yellow x 
yellow 3°38; yellow x other colour 3°74) and Castle (yellow x yellow 
4°71; yellow x other colour 5°57). On the other hand, Durham’s 
figures warn one to be cautious as to one’s inferences. 
