106 Mr. G. P. Mudge. On the Hereditary — [May 8, 
Ist. 2 Or 4 +6 Cr 6 8. 
2nd. 2 Cr4+3 Cr5+2 Cr 6 0. 
srd. 3 Cr4+2 Cr 5+2 Cr 6 6+1 pigmented ae 
4th. 3 Cr 442 Cr 5+2 Cr 6 0. 
oth. 2 Cr4+1 Cr 5+3 Cr 6 041 pigmented eyes. 
—_— -—_— 
12 8 15 2 
It is to be noted in the first litter, notwithstanding that it is large, that 
the predicted Cr 5 type is not present. That in the first, second, and third 
litters the proportion of albinoes to pigmented individuals is as near as it 
possibly can be to expectation, with the odd numbers involved. That in the 
third and fourth litters the albinoes are in excess. 
These considerations show us, what is also shown in others of my experi- 
ments, that predicted types will not necessarily appear in any one litter, and 
that large numbers must be reared before expected Prope ee in all cases 
will be quite accurately realised by actual results. 
Considering next, experiment 56, where the Cr 5 parent is known to be 
homozygote, the prediction is :— 
2 Cr 542 Cr 6 0. 
The actual result is :— 
A Cro 3 ©r, 0) 0: 
With the odd numbers concerned this is the nearest approach possible to 
prediction. The chief feature to notice is that while the predicted types 
have appeared, unpredicted ones have not. 
Experiments 58 and 59a may now be considered. The absence of albinoes 
in their offspring suggests that the Cr 5 parent was homozygous. The total 
offspring in these two experiments is 4 Cr 5+8 Cr606. Added to experi- 
ment 56, it gives a total of 8:11 respectively. There is thus, roundly, only 
one Cr 5 too few, and one Cr 6 0 too many. 
(3) “Trish” b x | Albino = Cr:'6b6 x Cr'4, 
Seven crosses of this nature have been made, 7.¢., experiments 60 to 66. 
All the “Irish” 6 parents used were descended from two individuals of the 
black variety wild grey rat (experiments 47 and 48). Five of the seven 
were from mating 47, and the remaining two from mating 48. 
Three of the albinoes used (experiments 60, 62, and 63) were also derived 
from the same albino parents, which were obtained from ordinary dealers. 
In experiment 61 the albino parent was also obtained from the same source, 
but from a different parentage. Their zygotic composition may therefore be 
represented by cgBsP. In experiments 64, 65, and 66 the albinoes used were 
