144 THE BUTTERFLIES OF NEW ENGLAND. 



ofrlulv, it would ap})c;ir as if two years must be required for the full cycle 

 of changes, and that the winter is [)assed in two conditions, both larval, 

 one just hatched or in a very early stage, the other full grown, or very 

 nearly full grown, a whole season being required for the development of 

 the larva alone. No one would be sur[)rised at this if he were to ex[)eri- 

 ence the conditions under wliicli these hardy creatures \u\\e to Ii\e. 



Such a cycle of changes, though unprecedented among our butterflies, 

 so far as their history is known, is supposed by some to be eqiuvlly true of the 

 alpine Oeneis aello, the young caterpillars of which are born at a like [)eriod 

 and hibernate without feeding. If this were its regular habit, we ought to 

 expect that, as is stated by some to be true of aello, the Ijutterfly would fly 

 only in alternate vears in any one spot. But not only is this not true of 

 oiu' species, but no fluctuation in its numbers has ever been noted. It 

 follows that if a period of two years is normally required for its transfor- 

 mations, there must be or have been some irregularity in its development 

 by which a regular annual series of perfect forms should appear. If in the 

 past only, then the Ijutterflies of the even years have no innnediate genetic 

 connection with those of the odd years, and two jtarallel series are li^■ing 

 on tiie same ground, subject to the same vicissitudes or to only such varia- 

 tions in them as alternate seasons may chance [)roduce. If this should 

 pro\e to be true, a very neat problem would be set before the modern 

 evolutionist to determine, first, how such a condition of things came about, 

 and second, what eflect isolation has had toward develo})ing two types of 

 butterflies. 



A few facts, however, lead me to believe that while a biennial cycle is the 

 rule, there are certain exce[)tions to it every year, by which a perfect com- 

 mingling of blood ensues and Nature protects itself against the danger of 

 extinction that niif>:ht ensue if one stance of larval existence were less able than 

 another to contend with the difficulties of an exce[)tional season. Dr. 

 Harris gives "June and July" as the season of the flight of the imago, the 

 former date on the authority of the botanist, Oakes, who found them abun- 

 dant in June, 1(S2(). The part of the month does not appear from Dr. 

 Harris' notes and 1 ha\e always supposed it referred to the closing- 

 days of the month until LSHH, after an excursion up the mountain in 

 company with Mr. Roland Hayward, on June (i. Between us we saw, on 

 no less than three different occasions in the al[)ine belt, a Le})idopteron which 

 in each instance the observer thought was semidea ; in the last case, the size, 

 the flight, and the color were observed by me for at least fifteen seconds 

 in broad daylight, at the nearest distance of just out of reach of my net ; and 

 were it not for the uuex[)ccte(lness of tlie appai'ition, I sliould not have had 

 the slightest doubt of its being semidea, for I know of no moth then flying 

 therefor u hicli it could have been mistaken. It is possible, therefore, that 

 Oakes also saw them early in Jiuie (when visits to the sununit are exces- 



