14 THE COMMONER BUTTEUFLIES. 



ter variation may occur in a single species having several 

 broods, in which an increasing proportion of each succes- 

 sive brood of chrysalids of one season pass over the ensuing 

 winter. Instances are on record in wliich chrysalids, nor- 

 mally hibernating, have been known to pass over a second 

 winter and then give birth to the butterfly. 



9. The Geneeal Histoey of Butteeflies. 



Beginning life as an Qgg which usually hatches within 

 a few days after being laid, the young caterpillar finds 

 its sole duty to be to eat and escape being eaten. It 

 feeds voraciously, and outgrows its skin so often that it 

 is obliged to moult four or five times before it is full 

 grown. On each of these occasions it stops feeding for a 

 while, spins a carpet of silk, and fastens its claws therein; 

 when the time for change comes, the old skin splits along 

 the middle of the back of the thoracic segments by violent 

 muscular effort, the old head-case (from which the new 

 head was first withdrawn) is shaken off and the creature 

 crawls out of its old skin, which in many instances it there- 

 upon devours. In the last change, to chrysalis, the head 

 is not removed from the old skin, but itself splits in the 

 middle and down one or both sides of the frontal triangle, 

 and the chrysalis emerges. After hanging awhile, the 

 chrysalis skin splits at much the same points and the but- 

 terfly emerges to begin the cycle again with the laying of 

 eggs. 



The cycle of changes through which a butterfly moves is 

 in temperate climates commonly passed once each year, — 

 or rather once each season, for it is winter that usually in- 

 terferes with the activities by robbing the creature of its 

 means of sustenance and paralyzing its action. Inasmuch 

 as the pupal stage is in the higher insects the period of 

 longest inactivity, one would presume beforehand that 



