182 THE ENTOMOLOGIST. 



in complete agreement as to the fact that the influence of a 

 higher temperature on the pupae makes our German butterflies, 

 which are alike in both broods, somewhat darker ; but my ex- 

 periments with a Neapolitan brood have proved that this brood 

 becomes red-gold through cold, and pow^dered with black through 

 heat, but that the latter character appears at a much lesser tem- 

 perature, and far more strongly than in the German brood. One 

 cannot, therefore, forbear ascribing a somewhat greater sensitive- 

 ness for this colour reaction from temperature to the southern 

 colony of phloeas^ than to the northern, particularly since a long 

 subjection to a low temperature nevertheless permits the Nea- 

 politan brood to appear with more black on the margins of the 

 wings, than the German form ever possesses. Theoretically, 

 therefore, this statement of the fact can be expressed on the 

 ground of my theory of heredity somewhat in the following 

 manner : the determinants (Bestimmungsstucke) assumed in the 

 germ-plasm of the scales concerned have been a little altered in 

 southern colonies of the species in the course of generations by 

 the constantly recurring high temperature, so that they tend to 

 the formation of black scales in a stronger degree than with the 

 northern colonies of the species. But among the latter also 

 these determinants can be induced to form black scales, if they 

 are affected by a high temperature at the time during which the 

 formation of colour is going on in the wings, i. e. in the last days 

 of the jDupal rest. The alterations of the scale-determinants are 

 consequently twofold in this case ; on the one hand the climatic 

 temperature acts upon them so long as the}^ still enclosed in the 

 germ-plasm of the egg or the sperm, are contained in the repro- 

 ductive organs of the insect, and this operation of altering must 

 first be a minimal one, which only increases to a noticeable extent 

 by accumulation during a long course of generations ; were it 

 not so, the spring brood from Naples could not still be always 

 comparatively free from black powdering, as is the case. But 

 secondly, the temperature effects alterations in the scale-deter- 

 minants in question, when they are already enclosed in the 

 rudiments of the wings of the pupa, and are on the point of 

 forming the scales of the wing, and this effect is a very much 

 stronger one. But while the former must be transmitted from 

 one generation to another by the continuity of the germ-plasm, 

 and can therefore also gradually accumulate and increase, the 

 latter cannot be inherited, as the wings and wing-scales of a 

 particular individual die with it, and this accounts for the pure 

 golden colour of the spring form of the south. 



I might lay especial stress on Merrifield's observation, ac- 

 cording to which the last five or six days of the pupal period 

 are the critical ones, i. c for deciding on the colour which should 

 arise. 



Two of Merrifield's experiments (Nos. V. and VI.) appear to 



