EXPERIMENTS IN INHERITANCE. 167 
combined results of Cuénot, Castle, and Durham. Adding my own 
results to those of the other observers named, we find :— 
Yellow. Other pala: 
WucnOtge amie huss ey ht oes sad: aoe Ss 263 100 
Gastley (1910) y ef as 4) cers a) a py a fe 800 435 
Durham(lOl)- tee Be) ele 448 232 
LDDUDGIE ence Sy Wee Ole ao poeta Cem Oe area 72 _ 41 
Experimental Be ae: eaystaliry Bane Ws fae Serge Fat 1583 808 
Calculated: 2s:) teeth. me eee) 1594 Tell 
It is of interest to find this anomalous result confirmed from 
experiments with an additional independent strain of mice. 
(c) The number of young in a litter from yellow x yellow which 
survive to an age at which their colour is determinable is small, 
averaging only 3°64, as against 4°58 among mice of other colours. It 
is possible that this is associated with the hypothetical abortion of 
zygotes homozygous in yellow. Cuénot and Castle find a similar 
though smaller difference in size of family; but, on the other hand, 
Durham does not. (See Appendix A.). 
II. The table on pp. 168 and 169 shows a list of matings of yellow 
x other colour. One notes: 
(a) The 54 matings of yellow x other colour give 131 yellow: 
125 other coloured young, expectation being, on the supposition that 
all the yellows were heterozygous, 128: 128. 
(b) There were 36 yellow mice involved in the matings, of which 
11 were known from their parentage to be heterozygous. The 
remaining 25 were derived from yellow xX yellow, and one-third at least 
of these should have been gametically pure to yellow and have given 
only yellow young when mated to mice of any other colour. But all 
save one, and this had a couple of youngsters only, threw some other 
colour in addition to yellow. 
(c) Of the 25 yellow mice ex yellow x yellow 14 are recorded also 
in the list of matings of yellow X yellow, so that 11 remain to be added 
to the 26 of the other list, making 37 yellow mice of which both 
parents were yellow, and of which none, on being tested adequately, 
proved to be homozygous, though about a dozen should have been so, 
even assuming both the yellow parents to have been in each case 
heterozygous. 
(d) The number of young in a litter from yellow X other colour 
which survived to an age at which their colour was determinable 
averages 4°74, much the same as in the case of matings in which both 
parents are some colour other than yellow, where the average is 4°58. 
There is no reason associated with the theory of abortion of zygotes 
Y Y why this should be otherwise. There is, of course, no opportunity 
for the formation of such zygotes in-the mating of yellow x other 
colour. 
