572 



NA TURE 



[April 13, 1899 



seasonally dimorphic species present numerous intermedia'e 

 forms, and that these intermediate forms themselves vary ac- 

 cording to the vegetation and rainfall, " so that the extreme of 

 a rainy-season form from a district where the rainfall is great and 

 the vegetation dense, is much more pronounced than the extreme 

 of a rainy-season form from a district with slight rainfall and 

 sparse vegetation ; and these differences are even more marked 

 in the dry-season forms." The genera of Pieiinae dealt with in 

 this paper are Hiiphiiia, .Ippias, I.xias, 7'erias, and Teiaioiiis, 

 and seasonal dimorphism is shown to prevail largely in all of 

 them, so that the author feels warranted in materially reducing 

 the number of hitherto admitted species, contending that many 

 of these are palpably founded on mere seasonal variations. 



In 1S95, I had the pleasure of receiving from a valued friend 

 and correspondent in Natal, Mr. Cecil N. Barker, the M.S. of 

 an intere.sting paper he had drawn up, from many years' field 

 observations, on the seasonal variation of butterflies in that 

 colony and the adjacent territories. This paper, which was 

 published the same year,' proceeds on much the same lines as 

 that of Captain Watson's just noticed, but, instead of being 

 confined to the Pierins;, traces the occurrence of the phenomenon 

 throughout the suborder, indicating the following caseS, viz. 

 .Vcr.i-in.c i (in Acriea) ; Satyrina' 2 (in Myca/esis) ; Nympha- 

 lin.v 9 (I each in Alella, Jiiiwnia, Hypaiiis, Hamanumida and 

 Chara.xc$, and 2 each in Precis and Crenis) ; Lycitnida; 3 (in 

 Lyiaena, ; and Pierina.- 20 (9 in Teraio.'iis. 4 in Pieris, 3 each 

 in Eroiiia and Terias, and i in Herpaeiiia). In many of these 

 thirty-six cases the seasonal difl'erences and the occurrence of 

 intermediate specimens about the change of season are carefully 

 described ; and several instances are recorded of the pairing of 

 Piiris gidica with P. ahyisinua or with intermediate examples. 

 Mr. Barker's observations were decidedly in support of my own 

 published opinion as to the seasonal dimorphism of Haiuami- 

 mida diiiJalns, Herpaeiiia tiip/iin, Teraco/iis regina, T. speiiosm, 

 Pieris pig(a^ P. gidicOy Eroiiia cleodora^ and E, leda. 



Mr. Barker's paper was soon followed by one of equal 

 interest - contrilmted to our Transnctioin by Mr. G. A. K. 

 Marshall, who has a most wide and intimate knowledge of 

 butterfly-life south of the Zambesi. .Mr. Marshall, after ex- 

 pressing his concurrence with Mr. Barker's opinions on the 

 subject, proceeds to criticise with justice Dr. A. G. Butler's 

 rather random suggestion (Trans. En/. Soc. Land. 1895, 

 p. 519) that in the Acra'ina: the presence of a broad ajncal 

 black patch on the forewings indicates a wet-season form, 

 proving this idea to be wholly untenable, at any rate in 

 three of the five cases advanced by Dr. Butler. He goes on to 

 indicate the signs of seasonal variation in nine species of .-liraea, 

 and notably in the Mashunaland . /. ha/ali, where both sexes 

 vary strongly, and unlike the other known cases in the genus, 

 have the black spots larger in the dry. season than in the wet- 

 season form. To the numerous instances given by Barker he 

 adds two more in My(a!esis and eight more in Precis. The 

 latter are shown to offer a beautiful series of gradations in di- 

 morphism, from the four species P. imlalica, P. elgiva, I', 

 lugfla and P. artaxia, where — in addition to larger size and 

 more falcate forewings — the dry-season change is almost limited 

 to the dull withered-leaf colour and marking of the under5;ide ; 

 then to the two species P. ceryne and P. arc/iesia, where the 

 upperside as well presents considerable alteration both in colour 

 and marking ; and finally, to the species /'. simia and /'. 

 oclaviaiialalensis, where the suggested respective dry-season 

 forms P. iiiama and P. sesaiiiiis present such extreme disparity 

 in the aspect of both upper and under sides as to render it 

 almost incredible that they can belong to the same species as the 

 two wet-season forms in question. 



The actual rearing of the dry-season form of Teiias zoe from 

 eggs laid by the latter, and its proving to be (as had long been 

 anticipated) the butterfly known as 7". Iirigitia, is recorded in this 

 paper on the authority of that practised collector and i>bserver, 

 my friend Mr. J. M. Hutchinson, of Estcourt in Natal : and 

 early in 1 897, Mr. Marshall, writing from that locality, in- 

 formed me that he had succeeded in rearing three specimens of 

 Terjcolits aii.xo, a wet-season form, from eggs laid by T. lop/ia, 

 a dry-season butterfly. In each of these two Pierine cases the 

 close relationship of the seasonal forms was so manifest, that 

 all the circumstances of their occurrence led one to expect the 



' ■■ Nulcs on Seasonal Dimorphism of Rhopalocera in N'atal. (Trans 

 Knt. Soi. LoHfi.y 189s, p. 413.) 



' " Notes on Seasonal Dimorphism in South African Butterflies." (t>/. 

 cil., 1896, p. 551.) 



NO. 1537, VOL. 59] 



species-identity to be proved before very long ; but it was other- 

 wise in the case of Precis octavia-nalalensis and P. sesamus, 

 notwithstanding the significant facts — very close resemblance in 

 both larvx ami pupne, occasional pairing of the two forms, and 

 the existence of various intermediate examples — which favoured 

 a similar conclusion. Thus it was with no ordinary interest that 

 I received from Prof. Poulton Mr. Marshall's announcement, 

 in a letter dated June 1898, that in three cases he had bred P. 

 sesamus from the eggs laid by P. oclavia-natalensis, and that 

 I saw the actual specimens of parent and offspring in two of 

 the three cases, which had been sent to the Hope Depart- 

 ment of the Oxford University Museum. An excellent 

 account by Mr. Marshall of what he rightly describes as "the 

 most remarkable instance of seasonal variation as yet known" 

 was published in July last.' What makes the case so striking 

 is not alone the very great difference of the upperside — deep 

 salmon-red with black borders and spots in octavia-nalalensis, 

 and violaceous-blue streaked with black, and a continuous series 

 of salmon-red spots in scsainus — but that of the underside also — 

 almost the same as the upperside, but pinker in octavia-natal- 

 ensis, and very dark greenish bronze with black streaks in 

 sesamus. Owing to the latter disparity nothing could 

 be more different than the appearance of the two 

 forms when at rest, oclavia-nata/ensis being very con- 

 spicuous, while sesamus is well concealed ; • and this wide 

 divergence is associated with the differing haunts and habits 

 of the two forms. Mr. Marshall seems inclined to the view 

 that the wet-season form octavia-natalensis is the older one, 

 and that the dry-season form sesamus, with its distinctly 

 protective underside, may be the result of greater persecution — 

 in the scarcity of insects of other orders— during that season. 

 On the other hand, he suggests the possibility of the wet-season 

 naia/eiisis-(orm being in process of modification in mimicry of 

 the prevalent red black spotted .Icraeie of the same region, in 

 which case sesamus would have to be taken as the older form. 

 I consider the latter to be more likely than the former view, see- 

 ing how much less sesamus has diverged than octavia-natalensis 

 from the general pattern of the genus Precis.'' 



.\ noteworthy fact in Mr. Marshall's experience in this case 

 was that, while in the second instance recorded he reared an 

 example of sesamus from an egg laid by octavia-natalensis, he 

 also obtained, only five days later, from another egg laid by 

 the same mother, on the same day, a pure octavia-nalalensis. He 

 expressly states that the two larva? from which these amazingly 

 different butterflies resulted were reared from the egg under 

 precisely similar conditions ; and he adds that not a few similar 

 instances had come under his notice. This is sufficiently 

 remarkable, but it by no means exhibits the apparent extreme 

 of variation among the offspring of one mother : for Mr. de 

 Niceville (in a letter of June 13 last) assures me that in India 

 '•at the change of the season, in one brood, from one batch of 

 eggs laid by ime female, you sometimes get both seasonal forms 

 and all intermediate ones." * Such cases, like those of more or 

 less complete resistance to altered temperature, so frequent in 

 the experiments of Weismann and others, point very clearly to 

 the operation of some other factor than the degree of humidity, 

 or of temperature ; but it must be admitted that we are as yet 

 quite in obscurity as to its actual nature, and that our investi- 

 gations into seasonal dimorphism must be far more system- 

 atically and thoroughly prosecuted before conclusions of a satis- 

 factory character can be arrived at. 



While the observations already on record, to which I have 

 drawn attention above, render it beyond question that seasonal 

 dimorphism is of world-wide prevalence, it is at the same time 

 surprising— considering the great and increasing study devoted 

 to exotic butterflies of late years — that so very little is definitely 

 known of the actual range and conditions of its occurrence 

 beyond European limits. So far as the Pal.varctic Region is 



1 See "Seisonal Dimoiphism in Butterflies of the Genus /'f«/j, Doubl." 

 (.•I<i»r. and Mag. .Val. Hist. (7). ii. p. 30 (181)8). 



- The rarely. occurring intermediate examples, as 1 have pointed out 

 (" South Afr. Butt.," i. pp. 230,231, and 233,1887), exhibit a complete 

 gradation as respects both upperside and underside. 



3 The only other specits of Precis of the (Ktaz'iii pattern and colouring 

 is /'. simia (consiilercj l>y Mr. Marshall to be the wet-se.-ison form of the 

 dry-season P. cuama), and this species may possibly also l>e mimetic of the 



* It would be of the very sreat&st service to these inquiries if such a 

 series as this, the otTspring of one mother, could be preserved in iu 

 entirety, together with a full record of all the conditions bearing on the 

 case. Mr. de Niceville does not mention the actual species to which his 



