230 LETHARGY 



life must be attributed, like all other points in 

 their history, to the struggle for the perpetuity of 

 the species. Should disaster befall the advance 

 guard who have not halted by the way, the slug- 

 gards can take up the work ; the chances of sur- 

 vival are, not doubled perhaps, but greatly in- 

 creased. Nature seizes upon some phenomenon 

 in the life of each species and turns it to its ad- 

 vantage ; thus in the European Brenthis, it seizes 

 on the caterpillar's habit of hibernation when half 

 grown, and forces the spring brood of caterpillars 

 at that point in their growth to premature hiber- 

 nation, in which some continue throughout the 

 hot weather and until the following spring. Do 

 not all these strange phenomena, invariably look- 

 ing toward the surer survival of the species, point 

 to something superior to the mere forces of evolu- 

 tion, controlling and directing them ? Surely, if 

 hibernation be the pure result of physical causa- 

 tion — and nothing seems simpler than that — 

 where are the physical causes that first produced 

 premature hibernation in midsummer ? If it be 

 said that this is subsequently induced through in- 

 heritance by the habit of the alternating brood, 

 we may ask : Why does not this occur in Ba- 

 silarchia, which winters in the same stage, and 



