1 4 Studies in the Theory of Descent. 



I left them for three months, transferring them to 

 a hothouse on September nth, and there (from 

 September 26th to October 3rd) sixty butterflies 

 emerged, the whole of which, without exception 

 and most of them in an unusually strong degree 

 bore the characters of the winter form. I, at least, 

 have never observed in the natural state such a 

 strong yellow on the underside of the hind wings, 

 and such a deep blackish-green veining, as pre- 

 vailed in these specimens (see, for instance, Figs. 

 10 and n). The temperature of the hothouse 

 (12 24 R.) did not, however, cause the emer- 

 gence of the whole of the pupae ; a portion hiber- 

 nated, and produced in the following spring 

 butterflies of the winter form only. I thus suc- 

 ceeded, with this species of Pieris, in completely 

 changing every individual of the summer genera- 

 tion into the winter form. 



It might be expected that the same result could 

 be more readily obtained with A. Levana, and 

 fresh experiments were undertaken, in order that 

 the pupae might remain in the refrigerator fully 

 two months from the period of their transforma- 

 tion (9-ioth July). But the result obtained was 

 the same as before fifty-seven butterflies emerged 

 in the hothouse 12 from September igthto October 

 4th, nearly all of these approaching very near to 

 the winter form, without a single specimen pre- 



11 See Exp. ir, Appendix I. 



