166 REPORTS ON THE STATE OF SCIENCE.—1914. 
dilute conditions are allelomorphic, and may be represented by 
presence or absence of the factor D. 
Further, any of the above conditions may be present potentially, 
but remain undeveloped in absence of some colour-activating material 
which may be represented by factor C; in the absence of this factor 
the animal is an albino. 
A. The Inheritance of Yellow Coat Colour in Mice. 
In the first place, all my yellow mice appear to be heterozygous in 
respect of their yellow coat colour; none which have been fairly tested 
breeding true to yellowness, but on the other hand giving offspring 
which include, in addition to yellows, a proportion of individuals 
whose colour is other than yellow. Yellow is incompletely epistatic 
to black and chocolate. I find that, as Durham points out, black 
pigment may be present in the hairs of yellows throwing blacks, and 
chocolate pigment in the hairs of yellows throwing chocolates. 
Moreover, the degree of development of these other pigments in the 
hairs varies a good deal during the life of the animal. 
The tendency to abnormal fattening of yellow mice pointed out by 
Durham was also evident in the mice used by me. 
I arrange the matings which concern yellow mice in two tables: 
yellow x yellow, and yellowxother colour. The abbreviations in 
brackets indicate the immediate parentage of the mice concerned. 
Where the heterozygous nature of a yellow mouse is not shown in 
the table by its offspring a note is added of some additional mating 
showing it to be heterozygous (see tables on pp. 164, 165, and 168, 
169). 
I. In regard to the matings yellow x yellow given in the table 
on pp. 164 and 165 certain points may be noted: 
(2) Twenty-six of the mice used were derived from the cross 
yellow x yellow, and expectation was that at least one-third of 
these would prove to be true-breeding yellows. There are only two, 
however (marked with asterisk), which could possibly answer to this 
condition, and there is no evidence about them beyond that given in the 
table. It will be seen that they produced only two and three young 
respectively. Matings with other mice designed to test them 
gametically proved sterile. It would evidently be inappropriate to 
quote these as examples of mice homozygous in yellow. 
(b) The total number of offspring is 72 yellow and 41 other 
colour. On the theory that yellow-bearing gametes do not conjugate, 
one would expect the ratio 3 : 1, from which the calculated result of 
the above matings would be 84°75:28'°25, a very poor approximation 
indeed. On the alternative theory that the yellow-bearing gametes do 
actually conjugate but that the zygotes so produced perish before 
birth, one would expect the ratio 2:1, from which the calculated 
result would be 75°3:37'6, a very close approximation to the experi- 
mental figures. The latter suggestion, moreover, harmonises with the 
