74 THE ENTOMOliOGISt. 



measuring only 35 — 38 millim. across the wings in more than a 

 dozen examples. 



Although in the following exj)eriments no hybernation of the 

 larva occurred, yet, in contrast to the instances just given, indi- 

 viduals of A.fasciata were reared from eggs of the same pair as 

 above, after 142—163 days of larval and 25—31 days of pupal 

 existence, which measured 55 — 57 millim. in expanse ; and eggs 

 of L. jnni, L. (male 59, female 74 millim.), yielded descendants 

 expanding 65—68 millim. in the male and 84—86 milHm. in 

 the female after 150—172 days of larval feeding and 25—37 days 

 in the pupal condition. Here, that is to say, notwithstanding 

 the raised temperature, there appeared to be scarcely any curtail- 

 ment of the normal period of feeding — of course after deduction 

 (in the case of the latter) of the period of hybernation ; and this 

 condition led directly to an abnormal increase of size in these 

 individuals. However simple and comprehensible these facts 

 may appear, they are nevertheless worthy of note ; inasmuch as 

 these experimental results throw light on the mode of origin of 

 a large number of species. I will here only mention Argynnis 

 dia, L., Lasiocampa tremulifolia, Hb., Boarmia consortaria, F., 

 — all with short larval periods, — compared with Argynnis ama- 

 thusia, Esp., Lasiocampa populifolia, Esp., Boarmia roboraria, 

 Schiff., with long larval periods. The respective differentiation 

 of these species, which (apart from the well-marked divergence 

 in size) present so extraordinarily close a resemblance to each 

 other both in the imaginal aspect and also to some extent in that 

 of the earlier stages, has probably resulted, according to these 

 experiments, from the fact that in earlier periods of the earth's 

 history their ancestors while in the larval condition did not 

 react in the same manner to changes of temperature. The 

 differences between the pupal stages of L. tremulifolia and 

 B. consortaria (hybernating as pupae) on the one hand, and 

 L. populifolia and B. roboraria (rapidly emerging) on the other, 

 may have arisen as necessary consequences of and divergence in 

 the larval habit at the time of the estabhshment of the species. 



(2) The form and aiypearance of the perfect insects derived 

 from these larvae which have been forced by means of the raised 

 temperature into new biological conditions do not appear to 

 follow any universal laws. Among the species controlled in this 

 respect entirely by the conditions of their Kfe previous to ma- 

 turity, the most conspicuous differences of this kind are pre- 

 sented by the second and third brood of Lasiocampa populi- 

 folia, Esp., that is to say, its two varieties, (estiva, Stgr., and 

 autuninalis, Jaenich, both of which, and especially the latter, 

 show a more deeply indented border to the wings than does the 

 form resulting from hybernated larvae. It is, however, in those 

 cases in which Nature herself performs the experiments before 

 our eyes by rearing the particular species during both the cooler 



