212 
GENETIC STUDIES ON THE SILKW« IRM 
Normal 4. The dark normal ; in extreme case the "eye-spots" are deep- 
black, and the "frontal patch" enclosed by them is intensely dark brown, so 
that the "eye-spots" become apparently confluent, while the lightest examples 
of this subtype approaches to 3, but are distinguished from the latter by the 
darker "eye-spots" and a thicker distribution of the dorsal dots. Many inter- 
mediate forms exist between these two extremities (Figs. 39, 40, 41, 46). 
It must be admitted that the above classification is to some extent arbitra- 
ry, for two adjoining subtypes are often difficult to separate, fluctuating one 
into the other ; moreover, it is not impossible that the present classification 
may be unsatisfactory, and further subdivision is needed. 
The normal marking is a compound character, as stated elsewhere, being 
composed of the two factors P and Q. Experiments have been made with 
the object of bringing out the component which causes the variation of the 
normal marking. A few data are, however, sufficient to show that the 
variability of the normal is due to that of the Q, gene, whereas the P sub- 
serves as a negative factor or partial suppressor of the Q, pattern (p. 144). In 
fact, almost all the subtypes exactly corresponding to those of the normal 
are found in the quail. We will denote these quail subtypes by the symbols 
Q,'j Q,"> Q'> Q, 4 - The following data show the relation between normal and 
quail subtypes. 
A i8'i4 Plain x A 2 1 — 5' 1 4 quail (Q 1 ) 
I " 1 . 
A 258' 1 5 Normal (1) Plain 
239 52 
1 
I 1 
A 4ii'i5 Normal (1) Quail (1) 
258 83 
P 94-2^4 Normal (2) x A 18' 14 Plain 
1 
A i6/ r x 5 All normal (2) 
342 $ x A 255'i5 Plain g 
1 
f 1 
Normal (2) Normal (1) and plain 
230 218 
