244 DIGONEUTISM 



Swallow-tail, for instance, is triple brooded in the 

 south, and hibernates as a butterfly and perhaps 

 also as a chrysalis ; in the north it is double 

 brooded, and hibernates only as a chrysalis. 



Digoneutism or polygoneutism, then, is either a 

 device of nature for the better perpetuation of the 

 species, by varying the conditions of its existence 

 at any given time, and so multiplying the chances 

 of successfully meeting opposing or unfavorable 

 agencies ; or it is simply taken advantage of by 

 nature as a means thus to vary the conditions. 

 The particular problem difficult of solution which 

 it carries in its train is this : In some species — 

 and it would appear to be no very uncommon 

 occurrence, and to be found among moths as well 

 as butterflies — the result of summer dormancy in 

 the caterpillar or prolonged life in the chrysalis 

 is that, by some unexplained common impulse, the 

 caterpillars or the chrysalids that arouse after leth- 

 argy, and do not hibernate, more frequently than 

 otherwise do this at such a time that the resulting 

 butterfly flies with its nephews and nieces instead 

 of with its brethren and sisters, i. e., it bridges 

 over with considerable accuracy the interval be- 

 tween two generations in midsummer, just as hap- 

 pens from easily perceived causes when winter 



