102 Mr. G. P. Mudge. On the Hereditary [May 8, 
the Cr 7 in the two latter experiments (53 and 34) was not homozygote and 
was, perhaps, an “ Irish” @ (see Summary of Results, No. 5, p. 115). 
The Cr 2* types used in my experiments, and also the “ Irish” 0, were of two 
different origins, one form in each type resulting from a cross of a self-grey or 
a self-black respectively with a Cr 4, and in the other with a corresponding 
cross with a Cr 5. The possibility that the Cr 4 in the two former cases 
carried the piebald pattern determiner must not be overlooked. The homo- 
zygote nature of the Cr 5 in the eighth line of the column of matings above 
was tested by crossing it with a Cr 5 known to be carrying albinism recessive. 
No albinoes appeared in its offspring. 
D. EXPERIMENTAL RESULTS. 
(1) Trish” 6x Trish” b= Ci-6 0 GCr Gab: 
(a) Albino Parentage-—Seven matings of this kind have been made. Of 
the seven pairs of “Irish” 6 individuals used, two pairs (experiments 49, 50) 
were derived from a cross of a black var.: wild grey x albino, three (51, 52, 53) 
from a cross of an extracted black (Cr 7) x Cr 4, and two (experiments 54, 55) 
from a cross of “ [rish” 6 x Cr 5 carrying albinism recessive. 
The black variety of the wild grey rat may be regarded as a pure black 
and as equivalent to an extracted Cr 7. There is no possibility of its carrying 
the grey chromogen determiner, since grey is dominant to black. We may, 
therefore, consider experiments 49,50, 51, 52, and 53 together and regard them 
all as crosses of a Cr 7 x Cr 4. 
The parental albinoes of these “ Irish” 0 individuals were bred by me from 
albino grandparents, which were in turn obtained from ordinary dealers. 
Rats obtained from this source are nearly sure to be of piebald origin, though 
one of mine thus obtained for another experiment carried the self character, 
and another the grey chromogen. We may, therefore, assume that these 
albinoes were carrying the piebald pattern and black chromogen determiners. 
On this assumption we may represent the “Irish” 6 individuals used by 
the symbol CegBSsP. 
It will, perhaps, be as well in this particular cross to show how the predic- 
tions which are deduced are arrived at, and I will therefore give a table 
of the possible gametic combinations. 
Each “ Irish” 0 individual of the zygotic composition CegBSsP will, at the 
segregation of the characters, form gametes which will carry the combination 
of characters shown in the following symbols: CgBSP, CgBsP, cgBSP, 
cgBsP. There are thus 16 possible combinations between the four kinds of 
gametes. The combinations are shown in the subjoined Table [. 
* See footnote, p. 100. 
