148 SEASONAL CHANGES AND HISTORIES. 



opment of some caterpillars and the disposition 

 of chrysalids to winter early. Wherever in a 

 double-brooded butterfly the second brood is less 

 abundant than the first, it is probable that the 

 butterfly is partly single and partly double 

 brooded that is, that the early brood of a given 

 year is made up of the direct descendants of each 

 brood of the preceding year. 



Occasionally, the difference in the number of 

 broods affects the mode of hibernation. The 

 Black Swallow-tail (Princeps Polyxenes), for in- 

 stance, is triple-brooded in the south, and hiber- 

 nates as a butterfly and perhaps also as a chrys- 

 alis ; in the north it is double-brooded, and hiber- 

 nates only as a chrysalis. 



To return again to our Meadow Fritillary with 

 its curious history. Should the season be so long 

 that the second brood of the vernal series could 

 lay eggs, these eggs would at once hatch, for their 

 normal period being often as short as five days, 

 weather which could induce a butterfly to lay 

 eggs would at once ripen the embryo ; the cater- 

 pillars would then be forced to hibernate in the 

 same condition as those of the aestival series, and 

 become members of that series the next year ; 

 while the vernal series would be kept up by 

 means of those caterpillars of its first brood 

 which, in the previous year, had gone into pre- 

 mature hibernation. Thus the vernal series 



