138 Mr. F. Merrilield's systematic temperature 



temperature, and therefore some of the colourmg must 

 be attributable to individual and presumably hereditary 

 qualities ; but I do not think any one can look at the 

 moths experimented on without recognising that practi- 

 cally the spotting or the spotlessness of antamnaria 

 depends on the temperature to which the pupa is ex- 

 posed, and that the temperature of an ordinary English 

 summer is low enough to develop plentiful spotting, 

 a difference between 65^ and 80° counting for much 

 more in this respect than one between 33° and 65°. 

 So that a continental pupa imported young might be 

 expected to develop the well known spotted appearance 

 of the dark British form ; in other words, the dark 

 northern form is not, or at all events may not be, 

 racial, but is the effect of climate on the individual 

 pupa. In this respect the species seems to differ alto- 

 gether from the double-brooded ones experimented on 

 by Prof. Weismann and Mr. Edwards. 



(ii) With alniaria {formerly tiliaria) (Tables XII., 

 XIII., XIV., XV., XVI.).— I tried on a brood of these, all 

 proceeding from the same parent, the same experiments 

 as on autnmtiaria ; but the results on the colouring, 

 though tending in the same direction, were by no means 

 so regular or so striking. This is, perhaps, partly 

 because I bred only 8 of the female sex (which is the 

 one which seems the most affected in this species) ; the 

 same accidental raising of the temperature, which was 

 so injurious to autumnaria, having been still more so to 

 alniaria. In those that were forced the larval period 

 averaged 27 days, the pupal 14 days, total 41 days ; 

 as against 62 days larval, and 23 pupal, total 85 days, 

 in those that were unforced. The pupating larvte and 

 pupge seem to bear cold better than those of autumnaria ; 

 I bred two perfect males after an exposure for 50 days to 

 a temperature of 33°. 



(iii) With illustraria. — It will, perhaps, be remem- 

 bered that last year I showed some illustraria of which 

 the summer pupte had been iced 14 days, with the 

 result that they manifested a very slight change of 

 colouring in the direction towards that of the winter- 

 pupated form. This year I determined to try the effect 

 of exposure to an icing temperature, for periods succes- 

 sively increased by regular steps. I wished to see 

 whether the colouring of the spring emergence could be 



