146 SEASONAL CHANGES AND HISTORIES. 



however, that it is a vain effort of nature to de- 

 velop a second brood, which in a more southern 

 climate, with a longer season, would prove suc- 

 cessful. 



But this we have said was the history of a part 

 only and probably of the smaller part ; the other 

 portion of the August caterpillars do not awake 

 from their lethargy at all until another season, 

 wintering as half -grown larvae, and finally reap- 

 pearing as butterflies the following June. 



Thus we have two series of individuals in the 

 same species, each single-brooded, or one making 

 an effort toward a second generation, which prob- 

 ably ends in disaster, or at most eventually feeds 

 the other series. 



In all plural-brooded butterflies with an exten- 

 sive distribution in latitude, the number of gener- 

 ations varies with the length of the season, and 

 this will account for the apparent waste we often 

 see as winter approaches, for such changes must 

 be gradual, and in intermediate districts irregu- 

 lar, dependent upon the season. Where such a 

 phenomenon occurs as that we noticed in the 

 Zebra Swallow tail [see Figs. 145-147], in which 

 some chrysalids of each brood live until the fol- 

 lowing spring, it manifestly makes little differ- 

 ence how short the season may be, or how sud- 



spring to the aestival series ; in which case the butterfly is gener- 

 ally single, occasionally double brooded. 



