32 Experimental Zoology 



central lines have partly disappeared, and the rest of the pattern 

 is less marked. The female of this first generation is shown 

 in Fig. 4. The wings are slightly transparent, with rarely a 

 darker mark on the upper surface. The insect is almost white. 



The caterpillars of the next generation were also fed on the 

 walnut. The male is shown in Fig. 5. The wings are whitish, 

 the marginal band has partly disappeared, and the transverse 

 lines are but slightly visible. The female is shown in Fig. 6. 

 The wings are transparent ; the V and the fifth of the marginal 

 points alone remain of the markings. 



The figures show a decided decrease in the size of the indi- 

 vidual, which is accompanied with a constitutional weakness. 

 It was not possible to obtain eggs from this generation. Pictet 

 resorted, therefore, to the device of feeding the first generation 

 on the walnut, the second on the oak, and then the third and 

 even the fourth on the walnut. When the first generation was 

 fed on the walnut and the second on the oak, the male moth 

 appeared as in Fig. 7, and the female as in Fig. 8. The fig- 

 ures show that the effects, produced by feeding the first genera- 

 tion on the walnut, persist during the second generation when 

 returned to the normal food. 



In another experiment the caterpillars were fed first on wal- 

 nut, then on oak, and then on walnut. The male was much 

 like that produced by two generations of walnut, as were the 

 females also. Another lot was fed walnut (ist gen.), oak (2d 

 gen.), walnut (3d gen.), walnut (4th gen.). The male type is 

 shown in Fig. 9. The wings are gray ash, or dusky; the 

 marginal points strongly marked, as well as most of the trans- 

 verse lines. The marginal band is accentuated in the four 

 wings. The females have white wings sometimes yellowish. 

 As in the male, the lines and the marginal band of the lower 

 wings is much accentuated. Thus while the greatest change is 

 effected by walnut, oak, walnut, there is a return to the darker 

 type if walnut is used again for the fourth generation. Pictet 

 interprets this as a return to the ancestral type; the result of 

 becoming accustomed to the walnut, and states that he has ob- 



