The Lnfluence of External Conditions 31 
The typical male and female moth of Ocneria dispar are 
shown in Fig. 1 and F ig. 2. In the male the wings are gray, 
ash, or dusky, with four zigzag black lines. The female is 
whitish gray or slightly yellow, with the same grayish white 
Fic. 4. Ocneria dispar: male, Fig. 1; and female, Fig.2. First generation fed 
on walnut leaves: male, Fig. 3; female, Fig. 4. Second generation fed on walnut: 
male, Fig. 5; female, Fig. 6. First generation on walnut, second on oak: male, 
Fig. 7; female, Fig. 8. First generation on walnut, second on oak, third on wal- 
nut, fourth on walnut: male, Fig. 9. (After Pictet.) 
pattern as the male, but more marked. The normal food is oak 
or birch. The young caterpillars can be made to eat the leaves 
of the walnut (Juglans regia), at first with difficulty, but the 
subsequent generations eat it with avidity. The male of the first 
generation is shown in Fig. 3. The wings are pale yellow, the 
