10 BRITISH BUTTERFLIES. 



period, supposed to be due to this difference in the size of the hiber- 

 nating larvae. More definite evidence is certainly wanted. Of the 

 larvae of the North American Phyciodes tharos, a many-brooded Melitaeid, 

 varying in its number of broods according to latitude, Scudder writes 

 (op. cit., p. 640) : ''Edwards finds that lethargy does not appear in the 

 earlier broods, but only in the last two broods of larvae, in West 

 Virginia, and, while invariable in those of the last brood, which winters, 

 and sometimes becomes lethargic as early as the end of August, .... 

 it also appears in the larvae of the preceding brood, some of which 

 become lethargic in very warm weather, while the greater number 

 proceed rapidly, like the larvae of the preceding broods, to pupation. 

 In the north .... caterpillars from eggs laid at the end of July 

 (and therefore of the second-brood of butterflies) all became lethargic 

 after the second moult (about September 4th) ; but, two weeks later, part 

 of them resumed activity, fed a few days, passed another moult, and then 

 became lethargic again ; these were placed in a cellar, and remained 

 without change through the winter. On another occasion, eggs laid 

 in the middle of August in Coalburgh, were taken to the Catskills, 

 where they hatched on the 20th ; after the second moult, a portion, 

 about 40 per cent., became lethargic, while the remainder continued 

 their changes until the butterflies appeared (September 15th-26th), 

 and some of the chrysalids, kept in a cool place in Albany, produced 

 imagines between October 2 1 st and November 2nd .... It is 

 interesting to note that about one-half of the 40 per cent, that became 

 lethargic began to feed again about September 26th, passed another 

 moult, and then resumed their lethargy. A third experiment showed 

 that eggs, laid in the Catskills at the end of June, by butterflies of 

 the first brood, and carried to West Virginia, hatched there on July 3rd, 

 most producing butterflies by the end of the month, but that a portion 

 (about 5 per cent.), even in this southern locality, became lethargic 

 after the second moult, a thing which Edwards had not found to occur 

 with native West Virginian larvae at that season. This leads him to 

 conclude that, probably, a portion of the caterpillars from the first brood 

 of butterflies in the north become lethargic, and continue so until the 

 following spring, i.e., that, in the north, the species is partly mono- 

 goneutic and partly digoneutic, and that, in the northernmost part of 

 the range, to judge from the short season and dates of flight of the 



butterflies, it is monogoneutic only This conclusion is in 



the highest degree probable, and the proportion of the caterpillars 

 from the first brood of butterflies which develop directly into the 

 second as we pass southward from the north, would be a very interest- 

 ing subject for investigation." We may assume that, in the Nearctic, 

 as in the Palaearctic, region, the variation in number, or proportion, of 

 individuals that go on to form a partial double- or triple-brood, even 

 at the same latitude, would, in different years, depend greatly on the diffe- 

 rence in individual seasons ; at least, this is so in western Europe. 

 Edwards is quoted (Butts. New England, i., p. 700) as stating that, " in 

 the wintering webs of Euphydryas phaeton, he invariably found a small 

 percentage of larvae which had not passed the third moult," the bulk of 

 the hybernating larvae having done so and reached the 4th stadium, but 

 Scudder could not confirm this ; he had only observed hybernating 

 larvae to moult once (not some once and others twice) in the spring. 

 Scudder thinks that the phenomenon is to be attributed to the 



