THE ENTOMOLOGIST. 281 



half of the following May. The caterpillars were divided 

 into two groups, those composing one of which were fed ex- 

 clusively on elm, and the others exclusively on whitethorn. 

 The caterpillars spun up between the 5th and 18th of July. 

 No perceptible variation was observed in the larva?, cocoons 

 or pnpa3 of the two divisions. The males in both divisions 

 began to hatch on the 18th of July, but the females did not 

 appear until half the males were already hatched. Almost all 

 the males in both divisions were fully developed, only two 

 cripples appearing out of the thirty-two fed upon elm. The 

 males fed on elm averaged one inch and five-twelfths in the 

 expansion of their fore wings : they were uniformly coloured, 

 much darker and richer than the males fed on the whitethorn, 

 the dark markings on the fore wings were strongly defined, 

 the ground colour of these wings was also darker ; the hind 

 wings were reddish brown. The males fed on the hawthorn 

 were considerably smaller, averaging only one inch and two- 

 twelfths in expanse ; the ground colour of all their wings was 

 paler and grayer than in the others, but the markings of the 

 fore wings were generally well-defined. A few of the males 

 in each division were considerably smaller than the speci- 

 mens exhibited. In the elm-fed females fourteen out of six- 

 teen were crippled, with their wings not properly developed, 

 and even the other two were slightly crippled : they were not 

 so large as those of the hawthorn-fed larvae. Having been 

 impregnated by the males, none of these females deposited 

 eggs, although they pulled off the down from their tails and 

 fixed it in tufts in the box, after the manner adopted by 

 ordinary females of this species in the act of oviposition. Of 

 the whitethorn-fed females less than one-half were crippled, 

 and these were not generally so much crippled as the elm-fed 

 females. This experiment seemed to prove that had the 

 species depended solely on the existence of the elm-fed 

 individuals it would have become extinct ; whilst the smaller 

 size of the males of the hawthorn-fed group showed that even 

 amongst them (the females of which were so much better de- 

 veloped than the elm-fed ones) the principle of degeneration 

 had set in, and that it would have been very improbable that 

 a distinct phytophagic race or sub-species would have been 

 effectually produced. [Specimens similar to those exhibited 

 by Mr. Westwood have been reared by thousands in Londoa 



