SEASONAL DIMOEPHISM OF LEPIDOPTERA. 179 



On Feb. 12th, 1 Deilephila ewpliorhice. 



,, 15th, 3 ,, ,, 



,, 17th, 1 Sphinx pinastri. 



,, 20th, 1 Deilepldla euplwrhice. 



,, 21st, 1 ,, ,, 



,, 25th, 10 Vanessa levana (nine crippled). 



,, 26th, 1 ,, ,, (crippled). 



,, 28th, 1 Sj^hinx pinastri (crippled). 



I could not detect any departure from the normal marking or 

 colouring in any of the species which emerged in the incubator. 

 The influence of a temperature of 27-31° C. was nil on pupae 

 already several weeks old in relation to the form of the perfect 

 insect. On the other hand, the development was considerably 

 hastened with all, but, as is general in forcing pupae, in a very 

 irregular manner. 



VIII. General Part : Eecapitulation. 



Although I am far from considering the few experiments, 

 which I could here put forward, as sufficient for reaching a 

 decisive settlement of our opinions on seasonal dimorphism, yet 

 I cannot forbear arranging them, provisionally at least, in 

 reference to our general conceptions of the subject. When in 

 the year 1875 I first set about investigating the ways of this 

 striking and yot so long neglected phenomenon, I assumed that 

 it was to a certain extent obvious, that this kind of dimorphism 

 was everywhere a direct result of the various direct influences of 

 climate, principally of the temperature, as it affects in regular 

 alternation the spring and the summer brood of many-brooded 

 species. I had also well considered the other possibility, that 

 dimorphism connected with the time of the year might also 

 depend upon the indirect influence of the changing environment, 

 i.e. that it might depend upon adaptation to the varying environ- 

 ment of the butterfly according to the time of year. I then 

 said : " It is not inconceivable in itself, that phenomena occur 

 among the Lepidoptera analogous to the winter and summer 

 clothing of alpine and arctic mammalia and birds, only with the 

 difference, that the change in colouring does not arise in one and 

 the same generation, but alternately in different ones." But at 

 that time the fact that the uj^per side of butterflies, which is 

 usually not adaptive, can be very variable just in summer and 

 spring, sometimes more so than the adaptive under side, appeared 

 to me to contradict this adaptation of seasonal dimorphism. Yet 

 it was the fact that the one or the other seasonal form could be 

 produced artificially by the operation of a higher or a lower 

 temperature, i. e. the stamp of the winter form might be im- 

 pressed on the summer brood and vice versa. I therefore con- 

 cluded that it was the measure of heat, which was acting during 



