Appendix. 157 



that the generation which formerly hibernated advances 

 into the spring, the last of the summer generations at 

 the same time reaching the beginning of winter. The 

 latter would then hibernate in the pupal state, and would 

 sooner or later also assume the winter form through the 

 action of the cold of winter. We should, in this case, 

 have two generations possessing more or less completely 

 the winter form, the ancient winter generation now 

 gradually losing the winter characters, and the new win- 

 ter generation gradually acquiring these characters. 



In the reverse case, i. e.^ by a lengthening of the sum- 

 mer, we should have the same possibilities only with the 

 difference that the disturbance of generations would 

 occur in a reverse direction. In this case it might 

 happen that the former winter generation would 

 become the autumnal brood, and more or less preserve 

 its characters for a long period. Here also a new 

 winter generation would be produced as soon as the 

 former spring brood had so far retrograded that its 

 pupae hibernated. 



I am only too conscious how entirely theoretical are 

 these conjectures. It is very possible that observation 

 of nature will render numerous corrections necessary. 

 For instance, I have assumed that every species is able, 

 when necessary, to adapt any one of its developmental 

 stages to hibernation. Whether this is actually the case 

 must be learnt from further researches ; at present we 

 only know that many species hibernate in the egg stage, 

 others in the larval state, others as pupae, and yet others 

 in the perfect state. We know also that many species 

 hibernate in several stages at the same time, but we do 

 not know whether each stage of every species has an 

 equal power of accommodation to cold. Should this not 

 be the case the above conjectures would have to be con- 

 siderably modified. To take up this subject, so as to 

 completely master all the facts connected therewith, 



