fl SRST: RCN RE. SEN OE ea Ee ToT A a 
THE CURIOUS HISTORY OF A BUTTERFLY. 517 
_ depositions of eggs in place of one; moreover, the fact is suffi- 
ciently established, that some of the caterpillars of the vernal series + 
hibernate when half grown, after a period of lethargy and that the 
wstival series can only pass the wiriter as caterpillars just from the 
egg ; so too is the period of oviposition ; these facts being granted, 
and the apparition of the butterflies known to all observers as 
occurring at the times stated, any other interpretation seems 
impossible. 
In all plural-brooded butterflies, with an extensive distribution 
in latitude, the number of generations varies with the length of 
the season. I am not aware that the mode of this variation has 
ever been studied; are the changes sudden or gradual? and do 
they involve any waste of energy on the part of Nature, as-in 
Brenthis Bellona? A little consideration will show what the 
result would be in the species under discussion; 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 caterpillars would 
then be forced to hibernate as those of the æstival 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 
ood which, in the previous year, had gone into premature -hiber- 
nation. Thus the vernal series would continually feed the æsti- 
val; yet it would suffer no greater loss than it does at present in 
the practical sterility of the September butterflies; it would be 
Subjected to no infusion.of blood from the æstival series and any 
Variation of structure from the normal type of the species, induced 
by its isolation, would not be lost. Were the season still longer, 
the vernal series would become double-brooded and independent, 
the caterpillars having time to attain half their size before hiber- 
basen: the lethargic propensity would be retained only by the 
æstiyal series, which, by this time, would probably have assumed 
the position our vernal series occupied at the beginning. 
If, on the other hand, we suppose a shorter season, such as 
actually exists in some parts of the country where Brenthis Bellona 
Occurs, undoubtedly the first change would be the entire elimina- 
Hiss of the September butterflies and the hibernation of all the 
vernal caterpillars when half grown; this is probably the actual 
State of things in the cooler parts of Canada; but what would 
