206 THE CANADIAN ENTOMOLOGIST. 



It is not possible to say of butterflies at large exactly when one came 

 from chrysalis, or when it expired, but m the case of any species we observe 

 at a certain time of the year, with great regularity, fresh butterflies are on 

 the wing, and that in a few weeks only here and there can this species be 

 seen, the survivors being old, abraded of wing and broken. If a female 

 be now taken, on dissection there will usually be found a few eggs in the 

 abdomen, perhaps half a dozen, the remains of an original stock of 200 

 or more. Sometimes not a vestige of the eggs remain. Any collector 

 much in the field will often have seen female butterflies on the ground, 

 sometimes struggling, oftener dead, and if examnied these will usually 

 show no sign of violence, but plenty of old age and exhaustion. 



In the case of many-brooded species we observe that, periodically, 

 every few weeks a new brood has come, then that the butterflies are old 

 and scarce, and suddenly great numbers of fresh ones are flying. So that 

 in a certain number of weeks a whole generation has come and gone. 

 But the individuals of this generation which emerge earliest, and lay their 

 eggs soonest, will die first, and as the emergence occupies at least half the 

 whole period of the generation, we may say, if a generation is on the 

 wing six weeks, that three or four weeks would be the limit of existence 

 of any particular individual. In many species, in the latitude of West 

 Virginia and further south, there is a new generation on the wing every 

 month, and in such case a butterfly three weeks old would be a patriarch 

 among its kind. In New York and New England, where most species are 

 double-brooded at least, the duration of an individual life may be a trifle 

 greater, but no more, depending upon the time the eggs are laid. 



In the case of a seasonally-dimorphic species, and still more of a tri- 

 morphic species, like Papilio Ajax, we can fix the limits of duration of 

 one or more of the forms with some definiteness. In my section of West 

 Virginia the form Walshii is on the wing very early ; Telamonides appears 

 about a month later, but occasional Walshii fly as late as any Tehwwfi- 

 ides ; and by first of June the third form, Marcellus, appears, and almost 

 at once completely supplants the other two. In a few days not an 

 example of the other forms will be seen. I find many memoranda in my 

 note books bearing on this point. 



In a series of years, from 1871 to 1881, the first appearance of all the 

 forms of Ajax, and the last appearance of the two spring forms, is recorded 

 nearly every year^ 



