THE FACTORS OF EVOLUTION 



187 



manner. Their progeny were kept at the ordinary room tem- 

 perature of about 20 C. Of the resulting 173 butterflies most had 

 the normal appearance, that is, they had reverted to their original 

 form ; but seventeen of those that had emerged last exhibited the 

 characteristics of their parents. Other experiments undertaken 

 later with various species of Vanessidse produced similar results 

 (fig. 50). 



Here we have a 

 clear proof that 

 changed conditions 

 of life can produce 



changes that may be mm , \ 



transmitted to sub- B 



sequent generations. 

 If Weismann objects 

 that we are here not 

 dealing with a trans- 

 mission of acquired 

 characters, because 

 the cold did not only 

 change the body- 

 cells, but simultane- 

 ously also the germ- 

 plasm, we cannot 

 admit this objection 

 as relevant. The 

 qjuestion is not 

 whether changes 

 affecting the body- 

 cells are transmiss- 

 ible, but whether it is 

 possible for a change 

 in the conditions of 

 life to cause reactions 

 and changes in the 

 organism that can be 

 transmitted to the descendants. It is obvious that nothing 

 can be transmitted which is not deposited in the heredi- 

 tary substance of the body. But if the individual is able to 



FIG. 50. INFLUENCE OF TEMPERATURE DURING THE 

 PUPA STAGE UPON COLOUR AND DESIGN OF BUTTERFLIES. 



(1) Camberwell beauty (Vanessa antiopa L.}. 

 (2) V. antiopa L. v. hygicea Hdrch., obtained after 

 exposing pupa two hours twice a day for four days 

 to a temperature of 10 C. (after Lampert). 



