( xciv ) 



about seven to eight months, the other of a few weeks, and the 

 two phases, as will be seen, differing to such a degree physio- 

 logically, that the winter phase is killed by the temperature in 

 which the summer phase flourishes ; often differing also in 

 size, shape and colour, and I believe frequently in habits. 

 The winter phase appears to have much more in common 

 physiologically with the " year-lived " species, the summer 

 phase belonging on the other hand to the equatorial or the 

 Mediterranean type. 



Examples of winter pupai killed by warmth.' 1 ' 



Among these let me first mention the famous Araschnia 

 levana, much the most striking of seasonally dimorphic 

 European forms of butterfly ; the winter phase being on its 

 upper surface of a bright orange brown, mottled with black, 

 having a general resemblance to some of the little "fritillaries" 

 (Melitivas and the smaller Argynnids) so abundant in spring, 

 the summer phase black, with an oblique white band running 

 down both pairs of wings, much as it does with the common 

 Limeuitis Sibylla. The pupae of the summer phase respond to 

 temperature most readily, those forced emerging in about 

 six days with great regularity ; if on the other hand 

 cooled, they are retarded for a period of, it may be, 

 many months. To the effect of such cooling on the 

 facies of the imago allusion will be made later. In 1895, 

 between the 22nd and 29th August, I received from 

 various parts of Germany, North, Central, and South, many 

 hundreds of larvae of A. levana of various sizes from half- 

 grown or less upwards ; many were very kindly sent to me 

 from Freiburg by Prof. Weismann. These pupated from about 

 the 28th August to the 2nd September. A large number 

 were on pupation placed in the refrigerator at about 46°-50° 

 F. (8°-10° C.) for eight weeks, i.e. till 26th October, when 

 they were placed out of doors, batches being transferred at 

 about fortnightly intervals to incubators (at 92° F.(33° C.) and 

 80° F. (27° C.)— it made no difference which). Some were left 

 out of doors from pupation, and 53 of these emerged between 



* See Table II in Appendix, Experiment 1. 



