The Influence of External Conditions 21 



in general that cooled or iced pupae gave dark and much-spotted 

 moths, while "forced" pupae were pale and spotless or with 

 reduced spots. He states that the markings are affected by 

 long- continued exposure, especially during the early pupal period, 

 but the color is chiefly affected during the penultimate period. 



Standfuss has experimented on as many as 7000 individuals 

 in all. He determined that the period in the life of the pupa 

 when it is most sensitive to heat is at the beginning, although 

 it is best not to try to produce the effect too soon after the cater- 

 pillar has become a pupa. If exposed soon to extreme cold, the 

 pupae die ; but if exposed soon to heat the best results, i.e. the 

 most divergent forms, are obtained, although the mortality is 

 high. If the pupa is exposed -as soon as it can stand it to 

 extreme cold and then to heat, the heat-type is produced. In 

 other words, the cold delays the development so that the heat 

 produces the greater effect; for as soon as the temperature is 

 raised the development goes forward rapidly. To get the best 

 effect from cold, Standfuss found it advantageous to expose first 

 to low temperatures, then for 5 to 10 days to moderate cold 

 (11 to 14 C.), and lastly bring the pupae to room temperature. 



In his earlier work Fischer subjected the pupae for several 

 days to extreme temperatures of heat or of cold, but later he 

 found it better to subject the pupae two or three times a day 

 to the extreme temperatures during a period of n to 20 days. 

 This method applies particularly to extreme temperatures. For 

 a low temperature he used o C. or 3 C. or even 8 to 20 

 C. The high temperature was from 35 to 46 C. The more ex- 

 treme the temperature that the pupae will stand the greater the 

 effect produced. Thus temperatures between o and 20 gave 

 greater e % ffects than those between o and + 10. Tempera- 

 tures of 42 to 46 gave more striking results than those of 35 

 to 41 C. 



The most important result obtained by Fischer was to show 

 that the same aberrations are obtained by extreme heat and by 

 extreme cold. The result may seem puzzling, but it must be re- 

 membered that the coagulation of proteids, which is probably 



