1 2 Stiidies in the Theory of Descent. 



taken out at the end of four weeks. I started with 

 the idea that it was perhaps not so much the re- 

 duced temperature as the retardation of develop- 

 ment which led to the transformation. But the 

 first experiment had shown that the butterflies 

 emerged between 8 and 10 R., and conse- 

 quently that the development could not be re- 

 tarded at this temperature. 



A very different result was obtained from the ex- 

 periment made at a lower temperature. n Of twenty 

 butterflies, fifteen had become transformed into 

 Porima, and of these three appeared very similar 

 to the winter form (Levana), differing only in the 

 absence of the narrow blue marginal line, which 

 is seldom absent in the true Levana. Five butter- 

 flies were uninfluenced by the cold, and remained 

 unchanged, emerging as the ordinary summer 

 form (Prorsa]. It thus appeared from this expe- 

 riment, that a large proportion of the butterflies 

 inclined to the Levana form by exposure to a 

 temperature of o 1 R. for four weeks, while 

 in a few specimens the transformation into this 

 form was nearly perfect. 



Should it not be possible to perfect the trans- 

 formation, so that each individual should take the 

 Levana form ? If the assumption of the Prorsa or 

 Levana form depends only on the direct influence 

 of temperature, or on the duration of the period of 



11 See Exp. 9, Appendix I. 



