236 THE EFFECT OF TEMPERATURE 



the latter towards a black colouration." Weismann 

 thinks that the two varieties may have originated owing 

 to a gradual cumulative influence of the climate, the 

 slight effects of one summer or winter having been 

 transmitted and added to from generation to genera- 

 tion. Such a cumulative effect can be accounted for 

 satisfactorily by supposing that the temperature not 

 only affects the " primary constituents " of the wings 

 of each individual i. e., a part of the soma but also 

 the corresponding " determinants " of the germ-plasm 

 contained in the germ cells of the animal. 



Arguing from experiments on about 5000 pupse, 

 Standfuss * has endeavoured to classify under five dif- 

 ferent headings the effects which temperature changes 

 may produce in Lepidoptera. 



(1) They may give rise to seasonal forms having a 

 similar aspect to those occurring among the palsearctic 

 fauna at certain definite seasons of the year. For in- 

 stance, pupse of Vanessa c-album (Comma butterfly), 

 kept at 37 C., gave origin to the light coloured, yel- 

 lowish brown form of butterfly, especially pale on the 

 under surface, whilst those kept in a refrigerator pro- 

 duced the form with a considerably darker under side, 

 in many cases mingled with a moss-green tint. Also 

 this form had much more sharply defined markings, and 

 a more deeply indented margin to the wings. Both 

 these forms, be it noticed, occur in nature at the present 

 time. Again, by exposing pupse of P. machaon (Swal- 

 low-tail), to a temperature of 37 C. ? insects were ob- 

 tained which bore a perfect resemblance to those that 



* The Entomologist, vol. xxviii. pp. 69, 102, and 145. (Translated 

 from the German by Dr. F. A. Dixey.) 



