1907.] Transmission of certain Coat Characters in Rats. 101 
As a rule, the ventral white in the “ Irish” 6 form assumes the character of 
a longitudinal band extending from the chest at the level of the arms back 
to the umbilicus or farther. In general form, this band is narrow-triangular 
with its base in the pectoral region. In most cases, the two angles of the 
base extend off along the ventral surface of the arms and reach the carpal 
bands. In some instances, however, this extension is absent, and 'in others 
broken. The longitudinal band itself is often broken, or expanded in some 
parts, usually in the abdomina! region, and constricted in others, usually just 
anterior to the umbilical region. In the pattern thus produced there is often 
symmetry, but usually more or less departure from a strict symmetrical figure 
exists. 
In the “ Irish” a form, the ventral white in most cases assumes the shape 
of a very small triangular patch in the pectoral region, with its apex directed 
posteriorly. It suggests a reduced pattern of the “Irish” 6 form. Some- 
times an additional spot of white is present on the abdomen. 
Origin of the “ Irish” 6. 
The “Irish” 6 is a heterozygote and in my experiments has been produced 
in the following 10 different kinds of crosses :— 
(1) Black var. of wild grey (Cr 7) x Cr 4.* 
(2) Extracted black (Cr 7) x Cr 4. 
(Or 2 x Cr 2.7 
(4) Cr 2x Cr 4. 
(5) Cr 2x Cr 5 (carrying albinism recessive). 
(6) Cr 5x Cr 4, 
(7) “ Irish” 6x “Trish” 0 (Cr 6 0). 
(8) “Irish” 6x Cr 5 (homozygote), 
(9) “Irish” 6 x Cr 5 (carrying albinism recessive), 
(10) “Trish” 0x Cr 4. 
Of these, Doncaster has previously obtained “ Irish” 6 from Nos. 6 and 10, 
and also probably from crosses Nos. 2, 3, 4,5, and 7. In these latter crosses 
Doncaster had not, at the time they were made, distinguished between “ Irish ” 
b and a. But in the light of my experiments there can be no doubt his 
“Trish” forms from these crosses were of the sub-type 0. The origin of 
“Trish” 6 forms from crosses Nos. 1, 8, and 9, are, therefore, new. In addition 
to these, Doncaster also obtained this form from crosses of Cr 6 ax Cr 6 3, 
Cr 7x Cr 5,and Cr7xCr606. It is almost certain from his records, that 
* See footnote, p. 100. 
+ The Cr 2 forms are similar in their visible zygotic characters to the “Irish” 6, but 
are grey in colour. 
