INTRODUCTION. 15 



this period would coincide with winter ; and so it does in 

 a large number of cases. Yet among butterflies the ex- 

 ceptions to such a rule are not only exceedingly common, 

 but, as miglit be expected were there any departure, they 

 are very varied and winter is j^assed, by one species or an- 

 other, in every conceivable stage of existence, including 

 every part of caterpillar life. Indeed, cases are not un- 

 known, especially in high latitudes and altitudes, where more 

 than one season is required to bring a butterfly to maturity. 

 On the other hand, a large number of our butterflies, and 

 this is especially true southward, complete the cycle of their 

 changes twice or oftener in a season, and there are not a 

 few having an extended latitudinal range which vary in this 

 respect, having one or more broods in the northern part of 

 their range, and an added brood or more in the southern. 

 The end of the season generally surprising multiple-brooded 

 butterflies in all stages of existence, an opportunity has 

 easily arisen for every possible form of hibernation or 

 lethargic life, which accounts for the variation discoverable 

 in the lives of our butterflies, each form settling at last 

 upon that series of changes which is best fitted for it. 



10. Variation in the Butterfly. 



Like most creatures, butterflies, when they are found 

 over a wide territory, show great difference between indi- 

 viduals found in the extremes of the range, so that it is 

 sometimes difficult to tell, at least until collections are 

 made over the intervening country, whether specimens 

 from distant places should be regarded as distinct species 

 or as geographical varieties. The most skilled may make 

 mistakes for lack of proper material. 



But quite apart from this, butterflies appear to be ex- 

 ceptionally sensitive to the environment and to offer an 

 Tinusual amount of variation of a different sort ; for di- 



