SEASONAL CHANGES AND HISTORIES. 147 



denly and effectually any brood may be cut off ; 

 these chrysalids, and so the species, will survive. 

 That this phenomenon is more common than is 

 generally supposed is shown by the increasing 

 number of proofs brought forward of lethargic 

 tendencies in caterpillars and of persistent torpor 

 in many midsummer chrysalids. It is also indi- 

 cated by the variation in the numerical propor- 

 tions of different broods ; the winter is the 

 severest season, and consequently the spring 

 broods are ordinarily, and under simple condi- 

 tions would always be, less numerous than the 

 summer or autumn broods ; generally the broods 

 go on increasing in individuals as the season ad- 

 vances ; but in the Meadow Fritillary it is not so, 

 and we have seen the reason why ; for it is made 

 up of only a part of the previous brood. We see 

 similar phenomena in other butterflies without 

 knowing the cause, and it may be presumed that 

 these are butterflies which have not long enjoyed 

 the privilege of the later brood, or, in other words, 

 in which a part of the chrysalids fail to persist 

 until the following spring. In the case of our 

 Tiger Swallow-tail, which is found from Alaska 

 to Florida, we have a butterfly which is single- 

 brooded in the north and double-brooded in 

 New England ;. but the second brood is much less 

 abundant than the first, and the change as we go 

 north is probably effected by the lingering devel- 



