April 13, 1899] 



NA TURE 



569 



fourths of the pupa; produced, not the summer form prorsa — 

 as under natural conditions they would have done — but the 

 intermediate form porima (extremely rare in nature), three of 

 these being very nearly the pure winter form levana. Increasing 

 the period of exposure to cold to eight weeks did not materially 

 add to the extent to which the summer form was lost and the 

 winter form substituted. The converse experiment, freijuently 

 repeated, consisted in placing in a hot-house (temperature 

 i2°-24° R.) immediately after pupation, pupa; from eggs laid 

 by the August brood of the summer form, prorsa ; but here the 

 artificial temperature had little or no effect, all, or nearly all, the 

 pupa: hibernating, and emerging in the following spring as the 

 pure winter-form /c-'ana. This latter result led the author to the 

 opinion that cold and warmth could not be the immediate 

 causes of a pupa emerging in the prorsa or kvana form ; and 

 that the explanation of the facts seemed to be [a) that the 

 winter form levana is the original type of the species, seeing 

 that it was found possible to make many specimens of the 

 summer ioxxn prorsa revert to it by means of cold, whereas the 

 converse change could not be effected ; and {h) that the species 

 originally existed in the glacial period as a single-brooded and 

 monomorphic butterfly, and only became double-brooded and 

 gradually developed the prorsa form as warmth of climate 

 increased. 



With Pietis iiapi, Weismann found the pupa; from eggs laid 

 by the winter form much more responsive to the action of cold 

 (applied immediately after pupation and continued for three 

 months) than those of A. kvana, by far the larger number 

 emerging as the pure winter form when transferred to a hot- 

 house, and the remainder (which resisted forcing and hibernated) 

 all producing the same form in the following spring. The con- 

 verse experiment was not tried with the pupa- of ordinary 

 P. iiapi, but with those o( the Alpine and I'olar variety, 

 bryoniae, but the result was in accordance with that of the 

 corresponding experiment in the case of A. Uvana — the applica- 

 tion of heat had no transforming effect, and all the butterflies 

 emerged as pure bryoniae. Weismann was thus led to regard 

 the single-brooded variety bryoniae as the original form of the 

 species from the glacial period, and napi in its winter and 

 summer forms as gradually produced under increasing climatic 

 warmth. 



The experiments conducted with so much skill and persever- 

 ance by W. H. Edwards with the North-American Papilio 

 ajax and Phydodes tharos yielded much the same results as 

 those obtained by Weismann in Europe. In the complicated 

 case of P. ajax — where the winter form presents itself in the 

 two differing generations known as -imlshiiaxiAlelamoiiides, and 

 the summer form known as marcellus appears in three similar 

 generations — Mr. Edwards, by the application of ice for a 

 period of two months, found that fifty pupce reared from eggs 

 laid by the second generation of the winter form {teloinouides), 

 which under natural conditions would nearly all have given the 

 summer form manellus, produced no fewer than twenty-two 

 telai)ionideSy one specimen intermediate between /f/trwt?;//^*'.^ and 

 walshii, eight examples intermediate between lelaiiioiiides and 

 marccMtis, but nearer to the former, eight intermediate between 

 the same forms but nearer to the latter, and only eleven true 

 marcellus. It should be oliserved, however, that there is a 

 difference in the .shape of the wings between the winter and 

 summer forms of this Papilio, and that the strong innate 

 tendency of the progeny of the winter form to assume the 

 summer form was evidenced in the fact that all the butterflies 

 from the refrigerated pu]xe which had the markings of tela- 

 iiionides or of walshii yet bore the shape of marcellus. 



The extreme variability of Phyciodes lliaros renders it difficult 

 to follow the details of ICdwards' experiments with the various 

 broods from different districts, but it is clear that, as in the ca,se 

 of P. aja.x, the application of cold induced the summer form to 

 revert to the winter form (marcia). I do not gather that the 

 converse experiment was tried with this butterfly ; but it was 

 attempted to a certain extent with Papilio ajax, whose hiber- 

 nating pupae were subjected to a moderate degree of heat during 

 some months, for several years in succession, without any change 

 being effected in the resulting winter form of the butterfly. The 

 evidence in the case of Grapta iii/errogationis has a different 

 bearing on the subject, seeing that this species does not hibernate 

 as pupa but as imago, and that therefore there is not, strictly 

 speaking, any "winter" form ; but it would appear that the 

 first of the four broods in the year consists wholly of the form 

 named umbrosa and the fourth of the form named fahricii, 



NO. 1537, VOL. 59] 



while the intervening second and third broods are each com- 

 posed of both forms. 



Only brief reference is made by Weismann to the experiments 

 on Aiascliiiia levana made by G. Dorfmeister,' an account of 

 which was published as far back as 1864, buta fulW/wfWc'of them 

 has been given by the late Prof Th. Eimer.^ Erom this I find 

 that, although, as Weismann points out, Dorfmeister did not 

 succeed — apparently from not employing a low enough tem|)er- 

 ature — in transforming the prnrsa-im\i\ into the Ie7iana-Uitm, 

 but obtained only some few of the intermediate form porima, 

 yet he was apparently repeatedly successful in the important 

 converse experiment (where Weismann's results were almost 

 negative), obtaining prorsa by means of warmth from Ihe prorsa 

 August brood. lie further obtained numerous gradations of 

 the intermediate form /»;////«, stages which under natural con- 

 ditions occcur so rarely that, during forty years' collecting, he 

 met with only a single specimen in the wild state in placeswhere 

 the forms levana and prorsa were quite common. Dorfmeister 

 was clearly the first to point out that temperature exercises its 

 chief influence during the act of pupation or shortly afterwards, 

 but he expressed his " inability to decide whether the modifica- 

 tions obtained were the direct consequence of the rise in tem- 

 perature, or only the indirect, depending on the shortening of 

 the time of development caused by the increased temperature." 



Eamiliar to all of us is the fine series of papers on temperature 

 experiments contributed to our Transaclions and Proceedinf^s, 

 to the Enlomologist, and to the Proceedings of the South London 

 Entomological Society by our Secretary, Mr. F. Merrifield ; 

 they are eight in number, the first having been published in 

 1S8S and the last in 1897.^ Mr. Merrifield's earlier experiments 

 were made with C'.eometrid moths of the genera Selenia and 

 Ennomos, certain species of which have normally two difteting 

 seasonal forms in England, and they extended to the application 

 of both icing and forcing for various periods in all stages from 

 egg to imago. The results were of much interest from many 

 points of view, and more especially as .showing (a) that the 

 continued application of low temperature to the pup.e reared 

 from eggs laid by the spring brood produced moths more and 

 more like their parents, instead of the natural summer fcjrm ; 

 (/)) that the opposite experiinent of applying heat to the pup:e 

 from eggs of the summer brood was fatal to a majority ol in- 

 dividuals, and produced in the survivors a proportion of the 

 summer form but mainly specimens intermediate only between 

 the spring and summer types ; (e) that it was in the pupal state 

 that temperatures exercised their chief influence; (d) that 

 forcing produced pale and comparatively spotless moths, while 

 cooling or icing produced dark and much spotted ones. Another 

 noteworthy |ioint was that the application of moishire in com- 

 bitiation with various temperatures to the pupa; of S. tetia- 

 lunaria and E. autuiiinaria had no effect on the resulting 

 moths. 



The dimorphic species next treated by Mr. Merrifield in 

 1892-93 were Pier is napi. Arose hnia levana, and Clirysoplianus 

 phlaeas. The results in the first and second of these species 

 were generally confirmatory of those obtained by previous ex- 

 perimenters. In the case of C phlaeas, which, though many- 

 brooded almost throughout its immense range, does not exhiliit 

 seasonal dimorphism in Europe except in Southern Italy, 

 Corsica and Greece, forcing caused on the upper side the diisky 

 suffusion and larger black spots of the forewings characteristic of 

 the southern summer form eleiis, while cold induced exactly the 

 opposite characters in the forewings, and also a great broadening 

 and radiation of the coppery band in the hindwings. In 1S96, 

 Mr. Merrifield ex]5erimented on jjupx of Picris daplidice, and 

 found that forcing produced the ordinary summer form, while 

 cooling for six weeks brought out the spring form bellidici. 



I have here only very briefly mentioned those of Mr. 

 .Merrifield's experiments which dealt with seasonally-dimorphic 

 species. His researches extended besides to upwards of twenty 

 monomorphic ones ; they were carried out with admirable skill, 

 care, and exactness of record, and the resulting phenomena — 

 especially in the species of Vanessa — were not only most 



1 " Ueber (let Einwirkunc vcrschiedenur wiihrend dcr Entwickclungs- 

 perioden [ingewendeter Wnrmc-gradc auf das F.-irbiing und Zcichiiung dcr 

 Schmelterlingc." (Mitthcil. Naturw. yereins /ilr Steiermark. 1864.) 



■-• " Ejitstefiung der Arteil auf Grund von Vcrcrben erwothcne Elgen- 

 sch.iflen nach dcr Geselzen organischcr Wacbscn.s" 1888. (Engl, transl., 

 by J. T. Cunningham, 1850, Sect. iv. pp. I3i-i34- ' have to thank Mr. 

 Murrificld for lending mc this work.) ...... 



^ For a most convenient /'r^eis and illustration of Mr. Mernneld s work, 

 by Dr. !■'. A. IJixey, see Nai im<i:, vol. Ivii. pp. 184-188 (1897) 



