i^YMPHALINAE: THE GENUS BRENTHIS. 585 



Yet Yiiudoiici- plainly says that tlie second brood of butterflies lays 

 eggs, and even gives the date of their deposition, with the complete his- 

 tory of the caterpillars hatched from them. 



Certainly the history of the European Brenthis is sufficiently strange, 

 yet that of our New P^ngland forms is equally remarkable, both in itself 

 and in its contrast with that of the European species. 



The first attempt to trace the history of our native species was made 

 more than fifteen years ago, when the statistics then at my disposal com- 

 pelled me to suggest a somewhat extraordinary theory, the outlines of 

 which, although no longer tenable, may be here sketched. According to 

 this view, our butterflies are single-brooded, although some of them pos- 

 sess three successive apparitions of the perfect form, and deposit their eggs 

 twice in the course of the same season. This phenomenon was explained 

 by the supposition that tliere were two sets of individuals, with cycles 

 of changes as independent as though the series were distinct species. 

 These two sets were designated the vernal and the aestival series, accord- 

 ing as the butterflies appeared in spring or summer ; for the season of the 

 two series do not correspond. The history of the vernal series corres- 

 ponds in part with that of the double brooded species in Europe, the 

 second generation being produced by uninterrupted descent from the 

 spring butterflies, while the latter are derived from half-grown hibernating 

 caterpillars of the previous year ; the eggs, however, being believed to be 

 never developed in the ovaries of the female until many weeks after her 

 eclosion (as in Argynnis), the autumnal brood of butterflies dies without 

 issue and therefore counts for nothing, as Doubleday has wrongly con- 

 jectured might be the case with the European species. The aestival series, 

 on the other hand, agrees with Argynnis almost completely, both in its 

 seasons and the modes by which these are produced, the larvae hibernating 

 as soon as born. The more striking features in the history of this group 

 in America , would then be as follows : — 



1. Two sets of individuals whose development is nowhere synchronous. 



2. Consequent difl^erence between individuals in their hiemal condition 

 (common to some other butterflies). 



3. Slow development of the egg (shared with Argynnis). 



4. Consequent longevity of imago (shared with Argynnis). 



5. Premature hibernation of the caterpillar. 



6. Abortive attempt on the part of one series to produce an autumnal 

 brood. 



Add to this that the European species differ from the American (1) in 

 the rapid development of the egg ; ( 2 ) in having only a single series of 

 individuals; (3) which is, properly speaking, double brooded; but (4) 

 whose progeny, through the lethargy or premature hibernation of the 

 earlier brood of caterpillars, unite in producing the spring butterflies, — 

 and an extraordinary chapter in the history- of insects would open before us. 



74 



