540 



NATURE 



[April 9, 1896 



United States of North America will do well to bear 

 in mind the success of fire conservancy in India. 

 Systematic forest management is a difficult undertaking, 

 which has many enemies. Nevertheless success is 

 possible, and if these forestry manuals facilitate the 

 attainment of success in this business, their authors will 

 have reason to be well satisfied with their work. 



Dietrich Brandis. 



THE DEVELOPMENT OF BUTTERFLIES 

 UNDER ARTIFICIAL CONDITIONS. 



THE effects which cold and heat, appHed to the pupa, 

 produce in the colours and patterns of the imaginal 

 Avings, have been studied for many years and by many 

 naturalists. Weismann in 1875 published an account of 

 his own experiments, and those conducted by others, in 

 an essay which was published in this country in 1882 

 among the " Studies in the Theory of Descent," trans- 

 lated and edited by Meldola. 



The experiments described by Weismann have been 

 repeated and greatly extended by Merrifield {Trans. 

 Ent. Soc. Lond., 1888, 1889, 1891, 1892, 1893, 1894), 

 while Dixey has published interesting observations on 

 the phylogenetic significance of some of the results 

 obtained {Ibid.., 1893, 1894). 



While these careful and successful experiments were 

 being conducted in this country, Standfuss of Zurich 

 has been independently engaged on the same research, 

 employing in many cases the very species which had 

 been used by Merrifield. Standfuss's paper, appearing 

 in 1894, has been translated by Dixey, and, after revision 

 by the author, has been published, with an introductory 

 note by Merrifield, in the pages of The Entomologist 

 for March, April, and May 1895. The editors of this 

 journal are to be congratulated on the effort they have 

 made to lay before their readers some of the interesting 

 results of entomological "research conducted by continental 

 naturalists. We may hope that the attempt which has 

 been so successfully made, will be frequently repeated. 



(i) The Egg. — The eggs of four species of moth 

 {Arctia fasciata, Dasychira abietis., Lasiocampa pruni, and 

 L. pini) were exposed to a high temperature, 34° C. 

 (93^ F.), as they were being laid, and subsequently up to 

 the time of hatching. The larvit hatched in two-thirds 

 or less of the normal time, and although the temperature 

 remained normal, 25° C. {']']'^ F.), throughout the sub- 

 sequent stages, 71 per cent, oi fasciata, 90 of abietis, 100 of 

 prtini, and 81 oi pifii emerged as imagos in that year, the 

 remainder hybernating as larvae ; as against 23, 12, 64, 

 and 28 per cent, respectively, when eggs from the same 

 parents had been laid and kept at a temperature of 22° C. 

 (72' F.) and at 25° C. during the subsequen^ stages. This 

 persistence throughout the later stages of the hurrying-up 

 of development, when the conditions which originally 

 started it had ceased at the beginning of larval life, is 

 very remarkable, and it is unfortunate that the author 

 should have contented himself with giving his results in 

 percentages instead of the actual numlDers obtained. 

 This criticism applies to nearly all the results recorded in 

 the paper. 



There was no evidence that the imagos were otherwise 

 influenced by the condition of the ova. 



(2) The Larva. — Experiments with an increased tem- 

 perature generally shortened the period of larval de- 

 velopment and reduced the size of the imago. From 

 these experiments the author infers that the great 

 difference in size between certain closely allied species 

 {e.g. Boarmia consortaria as compared with the much 

 larger B. roboraria) has been produced by the larvs re- 

 acting in a different manner under changes of tempera- 

 ture, so that some acquired long and the others short 

 larval periods. It would appear that the evidence in 

 favour of this conclusion has not been sufficiently sifted, 



NO. 1380, VOL. 53] 



and that certain obvious difficulties raised by this inter- 

 pretation have been overlooked. 



Certain changes in form, colour, and marking are also 

 described as following the temperature conditions of the 

 larvc^. In these cases, however, the author does not 

 appear to be giving the results of his own experiments, 

 but reasoning from the differences observed in the several 

 broods of many species appearing at different seasons, 

 and especially contrasting the forms produced from 

 hybernated larva; with those produced without hyberna- 

 tion. In these cases it is the duty of the naturalist to 

 determine by means of artificial experiments whether the 

 observed • changes are entirely due to conditions of 

 temperature, and whether the larval stage alone is of 

 importance. 



Many experiments were made with foods, polyphagous 

 larv^ being fed on poisonous or acrid plants, on such ab- 

 normal diet as raw meat, or on plants which had absorbed 

 solutions of various substances. The perfect insects 

 "often enough showed a failure in size or general 

 colouring, but in no case any noteworthy variation in tint 

 or pattern." 



The effects of light transmitted through glass of 

 different colours were negative, although the larvae were 

 exposed to these conditions " from the time when they 

 were quite small." 



(3) The Pupa. — By far the most complete results were 

 obtained by subjecting the pupa to various degrees of 

 temperature. 



The effects obtained with Papilio machaon and Vanessa 

 antiopa are of especial interest, inasmuch as Merrifield's 

 material had been inadequate and his results, as regards 

 these species, negative. 



Seventeen pupa; of P. machaon, kept at a temperature 

 of y]° C. (98^-99° F.) from the time when the cuticle 

 hardened at the beginning of pupation, produced in seven 

 to ten days fifteen insects, which were much lighter in 

 colour than usual, owing to the development of a yellow 

 powdering which obscured many of the dark markings on 

 the upper and under sides of the wings, and the body. 

 Changes in form are also described, including a marked 

 lengthening of the " tail " of the hind wing. " Some of 

 these specimens . . . bear a perfect resemblance to those 

 that fly in August in the neighbourhood of Antioch and 

 Jerusalem." The pupte subjected to cold (for twenty- 

 eight days) produced only two imagos, and these 

 resembled the Swiss and German forms emerging from 

 hybernated pupas. 



The pups of Vanessa atttiopa, after being exposed to 

 heat (37° C. or 98'-99" F.) for forty-eight hours, produced, 

 ten days later, butterflies in which the marginal blue ap- 

 peared to be reduced, and the yellow border broadened, but 

 in neither case to a greater extent than in nature. Among 

 these individuals, however, 2 per cent, presented a very 

 remarkable variation, which Standfuss has named var. 

 daicbi. This well-marked form is constantly produced 

 when the pupas were exposed to heat (as above) for sixty 

 hours, and then kept at a temperature of 24"^ C. (75^ F.). 

 Such pupa; produced the var. daubi in twelve days. The 

 upper surface of both wings is greatly darkened, becoming 

 almost black, the blue spots are much reduced and have 

 a violet tinge, but the most remarkable change occurs in 

 the yellow border, which is extremely darkened, so as to 

 leave, in extreme cases, only a small remnant of yellow 

 scales. The under side is as much darkened as the 

 upper ; and certain changes in the form of the wings are 

 also described. 



Cold produced very different effects according to the 

 time of exposure. The most interesting results, and those 

 which most strongly suggest the appearance of allied 

 species ( V. urticce, V. polychloros), followed the shortest 

 exposure of twenty-nine to thirty-four days in the 

 refrigerator. In these cases the brown ground colour 

 became lighter, and the blue spots (much enlarged on the 



