Chapter XIII: Introduction (1)

In the previous essay I attempted to trace a whole group of apparently “purely morphological” characters to the action of known factors of transformation, to explain them completely by these factors, and in this manner I endeavoured to exclude the operation of an internal power inciting change (phyletic vital force).

In this second study I have attempted to solve the problem as to whether such an innate inciting power can be shown to exist by comparing the forms of the two chief stages of metamorphic species, or whether such a force can be dispensed with.

Nobody has as yet apparently entertained the idea of testing this question by those species which appear in the two forms of larva and imago (insects), or, expressed in more general terms, by those species the individuals of which successively possess quite different forms (metamorphosis), or in which the different forms that occur are distributed among different individuals alternating with and proceeding from one another (alternation of generation). Nevertheless, it is precisely here that quite distinct form-relationships would be expected according as the development of the organic world depended on a phyletic vital force, or was simply the response of the specific organism to the action of the environment.

Assuming the first to be the case, there must have occurred, and must still occur, what I designate “phyletic parallelism,” _i.e._ the two stages of metamorphic species must have undergone a precisely parallel development--every change in the butterfly must have been accompanied or followed by a change in the caterpillar, and the systematic groups of the butterflies must be also found in a precisely corresponding manner in a systematic grouping of the caterpillars. If species are able to fashion themselves into new forms by an innate power causing periodic change, this re-moulding cannot possibly affect only one single stage of development--such as the larva only--but would rather extend, either contemporaneously or successively, to all stages--larva, pupa, and imago: each stage would acquire a new form, and it might even be expected that each would change to the same extent. At least, it cannot be perceived why a purely internal force should influence the development of one stage more than that of another. The larvæ and imagines of two species must differ from one another to the same extent, and the same must hold good for the larvæ and imagines of two genera, families, and so forth. In brief, a larval system must completely coincide with the system based entirely on imaginal characters, or, what amounts to the same thing, the form-relationships of the larvæ must correspond exactly with the form-relationships of the imagines.

On the other hand, the condition of affairs must be quite different if an internal power causing phyletic remodelling does not exist, the transformation of species depending entirely on the action of the environment. In this case dissimilarities in the phyletic development of the different stages of life must be expected, since the temporary, and often widely deviating, conditions of life in the two stages can and must frequently influence the one stage whilst leaving the other unacted upon--the former can therefore undergo remodelling while the latter remains unchanged.[169]

By this means there would arise an unequal difference between the two stages of two species. Thus, the butterflies, supposing these to have become changed, would bear a more remote form-relationship to each other than the caterpillars, and the differences between the former (imagines) would always be greater than that between the larvæ if the butterflies were, at several successive periods, affected by changing influences whilst the larvæ continued under the same conditions and accordingly remained unaltered. The two stages would not coincide in their phyletic development--the latter could not be expressed by parallel lines, and we should accordingly expect to find that there was by no means a complete congruity between the systems founded on the larval and imaginal characters respectively, but rather that the caterpillars frequently formed different systematic groups to the butterflies.[170]

Accordingly, the problem to be investigated was whether in those species which develope by means of metamorphosis, and of which the individual stages exist under very different conditions of life, a complete phyletic parallelism was to be found or not. This cannot be decided _directly_ since we cannot see the phyletic development unfolded under our observation, but it can be established _indirectly_ by examining and comparing with each other the form-relationships of the two separate stages--by confronting the larval and imaginal systematic groups. If the phyletic development has been parallel and perfectly equal, so also must its end-results--the forms at present existing--stand at equal distances from one another; larval and imaginal systems must coincide and be _congruent_. If the course of the phyletic development has not been parallel, there must appear inequalities--incongruences between the two systems.

I am certain that systematists of the old school will read these lines with dismay. Do we not regard it as a considerable advance in taxonomy that we have generally ceased to classify species simply according to one or to some few characters, and that we now take into consideration not merely the last stage of the development (the imago), but likewise the widely divergent young stages (larva and pupa)? And now shall it not be investigated whether caterpillars and butterflies do not form quite distinct systems? In the case of new species of butterflies of doubtful systematic position was not always the first question:--what is the nature of the caterpillars? and did not this frequently throw light upon the relationships of the imago? Assuredly; and without any doubt we have been quite correct in taking the larval structure into consideration. But in so doing we should always keep in mind that there are two kinds of relationship--form- and blood-relationship--which might possibly not always coincide.

It has hitherto been tacitly assumed that the degree of relationship between the imagines is always the same as that between the larvæ, and if blood-relationship is spoken of this must naturally be the case, since the larva and the imago are the same individual. In all groups of animals we have not always the means of deciding strictly between form- and blood-relationship, and must accordingly frequently content ourselves by taking simply the form-relationship as the basis of our systems, although the latter may not always express the blood-relationship. But it is exactly in the case of metamorphic species that there is no necessity for, nor ought we to remain satisfied with, this mode of procedure, since we have here two kinds of form-relationship, that of the larvæ and that of the imagines, and, as I have just attempted to show, it is by no means self-evident that these always agree; there are indeed already a sufficient number of instances to show that such agreement does not generally exist.

This want of coincidence is strikingly shown in a group of animals widely remote from the Insecta, viz. the Hydromedusæ, the systematic arrangement of which is quite different according as this is based on the polypoid or on the medusoid generation. Thus, the medusoid family of the oceanic Hydrozoa springs from polypites belonging to quite different families, and in each of these polypoid families there are species which produce _Medusæ_ of another family.

Similarly, the larvæ of the Ophiuroidea (_Pluteus_-form) among the Echinodermata are not the most closely related in form to those of the ordinary star-fishes, but rather to the larvæ of quite a distinct order, the sea-urchins.

I will not assert that in these two cases the dissimilarity in the form-relationship, or, as I may designate it, the incongruence of the morphological systems, must depend on an unequal rate of phyletic development in the two stages or generations, or that this incongruence can be completely explained by the admission of such an unequal rate of development: indeed it appears to me probable that, at least in the _Ophiureæ_, quite another factor is concerned--that the form-relationship to the larvæ of the sea-urchins does not depend upon blood-relationship, but on convergence (Oscar Schmidt), _i.e._ on adaptation to similar conditions of life. These two cases, however, show that unequal form-relationship of two stages may occur.

From such instances we certainly cannot infer off-hand that a phyletic force does not exist; it must first be investigated whether and to what extent such dissimilarities can be referred to unequal phyletic development and, should this be the case, whether deviations from a strict congruence of the morphological systems are not compatible with the admission of an internal transforming power. _That a certain amount_ of influence is exerted by the environment on the course of the processes of development of the organic world, will however be acceded to by the defenders of the phyletic vital force. It must therefore be demonstrated that deviations from complete congruence occur, which, from their nature or magnitude, are incompatible with the admission of innate powers, and, on the other hand, it must likewise be attempted to show that the departures from this congruence as well as the congruence itself can be explained without admitting a phyletic vital force.

In the following pages I shall attempt to solve this question for the order Lepidoptera, with the occasional assistance of two other orders of insects. Neither the Echinodermata nor the Hydromedusæ are at present adapted to such a critical examination; the number of species in these groups of which the development has been established with certainty is still too small, and their biological conditions are still to a great extent unknown. In both these respects they are far surpassed by the Lepidoptera. In this group we know a large number of species in the two chief stages of their development and likewise more or less exactly the conditions under which they exist during each of these phases. We are thus able to judge, at least to a certain extent, what changes in the conditions of life produce changes of structure. Neither in the number of known species of larvæ, nor in the intimate knowledge of their mode of life, can any of the remaining orders of insects compete with the Lepidoptera. There is no Dipterous or Hymenopterous genus in which ten or more species are so intimately known in the larval stage that they can be employed for the purposes of morphological comparison. Who is able to define the distinctions between the life-conditions of the larvæ of twenty different species of _Culex_ or of _Tipula_? The caterpillars of closely allied species of Lepidoptera, on the other hand, frequently live on different plants, from which circumstance alone a certain difference in the life-conditions is brought about.

The chief question which the research had to reply to was the following:--Does there exist a complete phyletic parallelism among Lepidoptera or not? or, more precisely speaking:--Can we infer, from the form-relationships which at present exist between larvæ on the one hand and imagines on the other, an exactly parallel course of phyletic development in both stages; or do incongruences of form-relationship exist which point to unequal development?

Before I proceed to the solution of this question it is indispensable that one point should be cleared up which has not been hitherto touched upon, but which must be settled before the problem can be formally stated in general terms. Before it can be asked whether larvæ and imagines have undergone a precisely parallel development, we must know whether unequal development is possible--whether there does not exist such an intimate structural relationship between the two stages that every change in one of these must bring about a change in the other. Were this the case, every change in the butterfly would cause a correlative change in the caterpillar, and _vice versâ_, so that an inequality of form-relationship between the larvæ on one hand and the imagines on the other would be inconceivable--systems based on the characters of the caterpillars would completely coincide with those based on the characters of the butterflies and we should arrive at a false conclusion if we attributed the phyletically parallel development of the two stages to the existence of an internal phyletic force, whilst it was only the known factor, correlation, which caused the equality of the course of development.

For these reasons it must first be established that the larva and imago are not respectively fixed in form, and the whole of the first section will therefore be devoted to proving that the two stages change independently of one another. Conclusions as to the causes of change will then be drawn, and these will corroborate from another side a subsequent inquiry as to the presence or absence of complete congruence in the two morphological systems. The two questions the answers to which will be successively attempted are by no means identical, although closely related, since it is quite conceivable that the first may be answered by there being no precise correlation of form, or only an extremely small correlation, between the caterpillar and the imago, whilst, at the same time, it would not be thereby decided whether the phyletic development of the two stages had kept pace uniformly or not. A perfect congruence of morphological relationships could only take place if transformations resulted from an internal power instead of external influences. The question:--Does there exist a fixed correlation of form between the two stages? must therefore be followed by another:--Do the form-relationships of the two stages coincide or not--has their phyletic development been uniform or not?

FOOTNOTES

[1] A most minute and exact description of the newly hatched larva of _Chionobas Aëllo_ is given by the American entomologist, Samuel H. Scudder. Ann. Soc. Ent. de Belgique, xvi., 1873.

[2] I am aware that this certainly cannot be said of philosophers like Lotze or Herbert Spencer; but these are at the same time both naturalists and philosophers.

[3] “Über die Artrechte des _Polyommatus Amyntas_ und _Polysperchon_.” Stett. ent. Zeit. 1849. Vol. x. p. 177-182. [In Kirby’s “Synonymic Catalogue of Diurnal Lepidoptera” _Plebeius Amyntas_ is given as a synonym and _P. Polysperchon_ as a var. of _P. Argiades_ Pall. R.M.]

[4] “Die Arten der Lepidopteren-Gattung _Ino_ Leach, nebst einigen Vorbemerkungen über Localvarietäten.” Stett. ent. Zeit. 1862. Vol. xxiii. p. 342.

[5] [Eng. ed. W. H. Edwards has since pointed out several beautiful cases of seasonal dimorphism in America. Thus _Plebeius Pseudargiolus_ is the summer form of _P. Violacea_, and _Phyciodes Tharos_ the summer form of _P. Marcia_. See Edwards’ “Butterflies of North America,” 1868-79.]

[6] [Eng. ed. I learn by a written communication from Dr. Speyer that two Geometræ, _Selenia Tetralunaria_ and _S. Illunaria_ Hüb., are seasonally dimorphic. In both species the winter form is much larger and darker.] [_Selenia Lunaria_, _S. Illustraria_, and some species of _Ephyra_ (_E. Punctaria_ and _E. Omicronaria_) are likewise seasonally dimorphic. For remarks on the case of _S. Illustraria_ see Dr. Knaggs in Ent. Mo. Mag., vol. iii. p. 238, and p. 256. Some observations on _E. Punctaria_ were communicated to the Entomological Society of London by Professor Westwood in 1877, on the authority of Mr. B. G. Cole. See Proc. Ent. Soc. 1877, pp. vi, vii. R.M.]

[7] [In 1860 Andrew Murray directed attention to the disguising colours of species which, like the Alpine hare, stoat, and ptarmigan, undergo seasonal variation of colour. See a paper “On the Disguises of Nature, being an inquiry into the laws which regulate external form and colour in plants and animals.” Edinb. New Phil. Journ., Jan. 1860. In 1873 I attempted to show that these and other cases of “variable protective colouring” could be fairly attributed to natural selection. See Proc. Zoo. Soc., Feb. 4th, 1873, pp. 153-162. R.M.]

[8] [A phenomenon somewhat analogous to seasonal change of protecting colour does occur in some Lepidoptera, only the change, instead of occurring in the same individual, is displayed by the successive individuals of the same brood. See Dr. Wallace on _Bombyx Cynthia_, Trans. Ent. Soc. Vol. v. p. 485. R.M.]

[9] “Über den Einfluss der Isolirung auf die Artbildung.” Leipzig, 1872, pp. 55-62.

[10] [Mr. A. R. Wallace maintains that the obscurely coloured females of those butterflies which possess brightly coloured males have been rendered inconspicuous by natural selection, owing to the greater need of protection by the former sex. See “Contributions to the Theory of Natural Selection,” London, 1870, pp. 112-114. It is now generally admitted that the underside of butterflies has undergone protectional adaptation; and many cases of local variation in the colour of the underside of the wings, in accordance with the nature of the soil, &c., are known. See, for instance, Mr. D. G. Rutherford on the colour-varieties of _Aterica Meleagris_ (Proc. Ent. Soc. 1878, p. xlii.), and Mr. J. Jenner Weir on a similar phenomenon in _Hipparchia Semele_ (_loc. cit._ p. xlix.) R.M.]

[11] [The fact that moths which, like the Geometræ, rest by day with the wings spread out, are protectively marked on the _upper_ side, fully corroborates this statement. R.M.]

[12] “Über die Einwirkung verschiedener, während der Entwicklungsperioden angewendeter Wärmegrade auf die Färbung und Zeichnung der Schmetterlinge.” A communication to the Society of Natural Science of Steiermark, 1864.

[13] See Exp. 9, Appendix I.

[14] See Exp. 11, Appendix I.

[15] See Exps. 4, 9, and 11, Appendix I.

[16] It seems to me very necessary to have a word expressing whether a species produces one, two, or more generations in the year, and I have therefore coined the expression _mono-_, _di-_, and _polygoneutic_ from γονεύω, I produce.

[17] [Eng. ed. In the German edition, which appeared in 1874, I was not able to support this hypothesis by geographical data, and could then only ask the question “whether in the most northern portion of its area of distribution, appears in two or only in one generation?” This question is now answered by the Swedish Expedition to the Yenisei in 1876. Herr Philipp Trybom, one of the members of this expedition, observed _A. Levana_ at the end of June and beginning of July, in the middle of Yenisei, in 60°-63° N. (Dagfjärilar från Yenisei in Översigt ap k. Vertensk. Akad. Förhandlingon, 1877, No. 6.) Trybom found _Levana_ at Yenisk on June 23rd, at Worogova (61° 5´) on July 3rd, at Asinova (61° 25´) on July 4th, at Insarowa (62° 5´) on July 7th, and at Alinskaja (63° 25´) on July 9th. The butterflies were especially abundant at the beginning of June, and were all of the typical _Levana_ form. Trybom expressly states, “we did not find a single specimen which differed perceptibly from Weismann’s Figs. 1 and 2 (‘Saison-Dimorphismus’ Taf. I.).”

The Swedish expedition soon left the Yenisei, and consequently was not able to decide by observations whether a second generation possessing the _Prorsa_ form appeared later in the summer. Nevertheless, it may be stated with great probability that this is not the case. The districts in which _Levana_ occurs on the Yenisei have about the same isotherm as Archangel or Haparanda, and therefore the same summer temperature. Dr. Staudinger, whose views I solicited, writes to me:--“In Finnmark (about 67° N.) I observed no species with two generations; even _Polyommatus Phlæas_, which occurs there, and which in Germany has always two, and in the south, perhaps, three generations, in Finnmark has only one generation. A second generation would be impossible, and this would also be the case with _Levana_ in the middle of Yenisei. I certainly have _Levana_ and _Prorsa_ from the middle of Amur, but _Levana_ flies there at the end of May, and the summers are very warm.” The middle of Amur lies, moreover, in 50° N. lat., and therefore 10°-13° south of the districts of the Yenisei mentioned.

It must thus be certainly admitted that on the Yenisei _A. Levana_ occurs only in the _Levana_ form, and that consequently this species is at the present time, in the northernmost portion of its area of distribution, in the same condition as that in which I conceive it to have been in mid Europe during the glacial period. It would be of the greatest interest to make experiments in breeding with this single-brooded _Levana_ from the Yenisei, i.e., to attempt to change its offspring into the _Prorsa_ form by the action of a high temperature. If this could not be accomplished it would furnish a confirmation of my hypothesis than which nothing more rigorous could be desired.]

[18] See Exp. 10, Appendix I.

[19] When Dorfmeister remarks that hibernating pupæ which, at an early stage “were taken for development into a room, or not exposed to any cold, gave dwarfed, weakly and crippled,” or otherwise damaged butterflies, this is entirely attributable to the fact that this able entomologist had neglected to supply the necessary moisture to the warm air. By keeping pupæ over water I have always obtained very fine butterflies.

[20] [For other remarkable cases of sexual dimorphism (not _antigeny_ in the sense used by Mr. S. H. Scudder, Proc. Amer. Acad., vol. xii. 1877, pp. 150-158) see Wallace “On the Phenomena of Variation and Geographical Distribution, as illustrated by the Papilionidæ of the Malayan Region,” Trans. Linn. Soc., vol. xxv. 1865, pp. 5-10. R.M.]

[21] [Eng. ed. Dimorphism of this kind has since been made known: the North American _Limenitis Artemis_ and _L. Proserpina_ are not two species, as was formerly believed, but only one. Edwards bred both forms from eggs of _Proserpina_. Both are single-brooded, and both have males and females. The two forms fly together, but _L. Artemis_ is much more widely distributed, and more abundant than _L. Proserpina_. See “Butterflies of North America,” vol. ii.]

[22] [Eng. ed. Edwards has since proved experimentally that by the application of ice a large proportion of the pupæ do indeed give rise to the var. _Telamonides_. He bred from eggs of _Telamonides_ 122 pupæ, which, under natural conditions, would nearly all have given the var. _Marcellus_. After two months’ exposure to the low temperature there emerged from August 24th to October 16th, fifty butterflies, viz. twenty-two _Telamonides_, one intermediate form between _Telamonides_ and _Walshii_, eight intermediate forms between _Telamonides_ and _Marcellus_ more nearly related to the former, six intermediate forms between _Telamonides_ and _Marcellus_, but more closely resembling the latter, and thirteen _Marcellus_. Through various mishaps the action of the ice was not complete and equal. See the “Canadian Entomologist,” 1875, p. 228. In the newly discovered case of _Phyciodes Tharos_ also, Edwards has succeeded in causing the brood from the winter form to revert, by the application of ice to this same form. See Appendix II. for a _résumé_ of Edwards’ experiments upon both _Papilio Ajax_ and _Phyciodes Tharos_. R.M.]

[23] Thus from eggs of _Walshii_, laid on April 10th, Edwards obtained, after a pupal period of fourteen days, from the 1st to the 6th of June, fifty-eight butterflies of the form _Marcellus_, one of _Walshii_, and one of _Telamonides_.

[24] [The word ‘Amixie,’ from the Greek ἀμιξία, was first adopted by the author to express the idea of the prevention of crossing by isolation in his essay “Über den Einfluss der Isolirung auf die Artbildung,” Leipzig, 1872, p. 49. R.M.]

[25] [Eng. ed. In 1844, Boisduval maintained this relationship of the two forms. See Speyer’s “Geographische Verbreit. d. Schmetterl.,” i. p. 455.]

[26] According to a written communication from Dr. Staudinger, the female _Bryoniæ_ from Lapland are never so dusky as is commonly the case in the Alps, but they often have, on the other hand, a yellow instead of a white ground-colour. In the Alps, yellow specimens are not uncommon, and in the Jura are even the rule.

[27] [According to W. F. Kirby (Syn. Cat. Diurn. Lepidop.), the species is almost cosmopolitan, occurring, as well as throughout Europe, in Northern India (var. _Timeus_), Shanghai (var. _Chinensis_), Abyssinia (var. _Pseudophlæas_), Massachusetts (var. _Americana_), and California (var. _Hypophlæas_). In a long series from Northern India, in my own collection, all the specimens are extremely dark, the males being almost black. R.M.]

[28] [Eng. ed. From a written communication from Dr. Speyer, it appears that also in Germany there is a small difference between the two generations. The German summer brood has likewise more black on the upper side, although seldom so much as the South European summer brood.]

[29] [Assuming that in all butterflies similar colours are produced by the same chemical compounds. R.M.]

[30] [Mr. H. W. Bates mentions instances of local variation in colour affecting many distinct species in the same district in his memoir “On the Lepidoptera of the Amazon Valley;” Trans. Linn. Soc., vol. xxiii. Mr. A. R. Wallace also has brought together a large number of cases of variation in colour according to distribution, in his address to the biological section of the British Association at Glasgow in 1876. See “Brit. Assoc. Report,” 1876, pp. 100-110. For observations on the change of colour in British Lepidoptera according to distribution see papers by Mr. E. Birchall in “Ent. Mo. Mag.,” Nov., 1876, and by Dr. F. Buchanan White, “Ent. Mo. Mag.,” Dec., 1876. The colour variations in all these cases are of course not _protective_ as in the well-known case of _Gnophos obscurata_, &c. R.M.]

[31] See Figs. 10 and 14, 11 and 15, Plate I.

[32] “On the Origin and Metamorphoses of Insects,” London, 1874.

[33] I at first thought of designating the two forms of cyclical or homochronic heredity as ontogenetic- and phyletic-cyclical heredity. The former would certainly be correct; the latter would be also applicable to alternation of generation (in which actually two or more phyletic stages alternate with each other) but not to all those cases which I attribute to heterogenesis, in which, as with seasonal dimorphism, a series of generations of _the same_ phyletic stage constitute the point of departure.

[34] When Meyer-Dürr, who is otherwise very accurate, states in his “Verzeichniss der Schmetterlinge der Schweiz,” (1852, p. 207), that the winter and summer generations of _P. Ægeria_ differ to a small extent in the contour of the wings and in marking, he has committed an error. The characters which this author attributes to the summer form are much more applicable to the female sex. There exists in this species a trifling sexual dimorphism, but no seasonal dimorphism.

[35] P. C. Zeller, “Bemerkungen über die auf einer Reise nach Italien und Sicilien gesammelten Schmetterlingsarten.” Isis, 1847, ii.-xii.

[36] “Isoporien der europäischen Tagfalter.” Stuttgart, 1873.

[37] [Trans. Linn. Soc., vol. xxv. 1865, p. 9. R.M.]

[38] It is certainly preferable to make use of the expression “metagenesis” in this special sense instead of introducing a new one. As a general designation, comprehending metagenesis and heterogenesis, there will then remain the expression “alternation of generation,” if one does not prefer to say “cyclical propagation.” The latter may be well used in contradistinction to “metamorphosis.”

[39] _Loc. cit._ chap. iv.

[40] The idea that alternation of generation is derived from polymorphism (not the reverse, as usually happens; i.e. polymorphism from alternation of generation) is not new, as I find whilst correcting the final proof. Semper has already expressed it at the conclusion of his interesting memoir, “Über Generationswechsel bei Steinkorallen,” &c. See “Zeitschrift f. wiss. Zool.” vol. xxii. 1872.

[41] See my essay “Über den Einfluss der Isolirung auf die Artbildung.” Leipzig, 1872.

[42] [In the case of monogoneutic species which, by artificial ‘forcing,’ have been made to give two generations in the year, it has generally been found that the reproductive system has been imperfectly developed in the second brood. A minute anatomical investigation of the sexual organs in the two broods of seasonally dimorphic insects would be of great interest, and might lead to important results. R.M.]

[43] “Grundzüge der Zoologie.” 2nd ed. Leipzig, 1872. Introduction.

[44] With reference to this subject, see the discussion by the Belgian Entomological Society, Brussels, 1873.

[45] P. E. Müller, “Bidrag til Cladocerners Fortplantingshistorie,” 1868.

[46] Sars, in “Förhandlinger i Videnskabs Selskabet i Christiania,” 1873, part i.

[47] [Eng. ed. Recent researches on alternation of generation in the Daphniacea have convinced me that _direct_ action of external conditions does not in these cases come into consideration, but only _indirect_ action.]

[48] See my memoir, “Über Bau und Lebenserscheinungen der _Leptodora hyalina_,” Zeitschrift f. wiss. Zool., vol. xxiv. part 3, 1874.

[49] Stettin. entom. Zeit., vol. xviii. p. 83, 1857.

[50] Compt. Rend., vol. lxxvii. p. 1164, 1873.

[51] [“Accidental” in the sense of our being in ignorance of the laws of variation, as so frequently insisted upon by Darwin. R.M.]

[52] [Eng. ed. Since this was written I have studied the ornamental colours of the _Daphniidæ_; and, as a result, I no longer doubt that sexual selection plays a very important part in the marking and colouring of butterflies. I by no means exclude both transforming factors, however; it is quite conceivable, on the contrary, that a change produced directly by climate may be still further increased by sexual selection. The above given case of _Polyommatus Phlæas_ may perhaps be explained in this manner. That sexual selection plays a part in butterflies, is proved above all by the odoriferous scales and tufts of the males discovered by Fritz Müller.] [For remarks on the odours emitted by butterflies and moths, see Fritz Müller in “Jena. Zeit. f. Naturwissen.,” vol. xi. p. 99; also “Notes on Brazilian Entomology,” Trans. Ent. Soc. 1878, p. 211. The odoriferous organs of the female _Heliconinæ_ are fully described in a paper in “Zeit. f. Wissen. Zool.,” vol. xxx. p. 167. The position of the scent-tufts in the sphinx-moths is shown in Proc. Entom. Soc. 1878, p. ii. Many British moths, such as _Phlogophora meticulosa_, _Cosmia trapezina_, &c. &c., have tufts in a similar position. The fans on the feet of _Acidalia bisetata_, _Herminia barbalis_, _H. tarsipennalis_, &c., are also probably scent organs. A large moth from Jamaica, well known to possess a powerful odour when alive (_Erebus odorus_ Linn.), has great scent-tufts on the hind legs. For the application of the theory of sexual selection to butterflies, see, in addition, to Darwin’s “Descent of Man,” Fritz Müller in “Kosmos,” vol. ii. p. 42; also for January, 1879, p. 285; and Darwin in “Nature,” vol. xxi. January 8th, 1880, p. 237. R.M.]

[53] Nägeli, “Entstehung und Begriff der naturhistorischen Art,” Munich, 1865, p. 25. The author interprets the facts above quoted in a quite opposite sense, but this is obviously erroneous.

[54] See my essay, “Über den Einfluss der Isolirung auf die Artbildung.” Leipzig, 1872.

[55] [Eng. ed. In the summer of 1877, Dr. Hilgendorf again investigated the Steinheim fossil shells, and found his former statements to be completely confirmed. At the meeting of the German Naturalists and Physicists at Munich, in 1877, he exhibited numerous preparations, which left no doubt that the chief results of his first research were correct, and that there have been deposited a series of successively derived species together with their connecting intermediate forms.]

[56] See my essay, “Über die Berechtigung der Darwin’schen Theorie.” Leipzig, 1868.

[57] I expressly insist upon this here, because the notice of Askenasy’s thoughtful essay which I gave in the “Archiv für Anthropologie” (1873) has frequently been misunderstood.

[58] The experiments upon _Papilio Ajax_ and _Phyciodes Tharos_, described in this Appendix, were made by Mr. W. H. Edwards (see his “Butterflies of North America;” also the “Canadian Entomologist,” vol. vii. p. 228-240, and vol. ix. p. 1-10, 51-5, and 203-6); and I have added them, together with some hitherto unpublished results, to Dr. Weismann’s Essay, in order to complete the history of the subject of seasonal dimorphism up to the present time.--R.M.

[59] This is a striking illustration of the diversity of individual constitution so frequently insisted on by Dr. Weismann in the foregoing portion of this work.

[60] The reader who wishes to acquire a detailed knowledge of the different varieties of this butterfly, of which a very large number are known, must consult the plates and descriptions in Edwards’ “Butterflies of North America,” vol. ii.

[61] Mr. Edwards has shown also that _Argynnis Myrina_ can lay fertile eggs when but a few hours out of the chrysalis. Canad. Ent., September, 1876, vol. viii. No. 9.

[62] Mr. Edwards remarks that the habit of becoming lethargic is of great service to a digoneutic species in a mountain region where it is exposed to sharp changes of temperature. “If the fate of the species depended on the last larval brood of the year, and especially if the larvæ must reach a certain stage of growth before they were fitted to enter upon their hibernation, it might well happen that now and then an early frost or a tempestuous season would destroy all the larvæ of the district.”

[63] Compare this with Weismann’s remarks, pp. 19-22, and 53.

[64] See Canad. Ent., vol. ix. p. 69.

[65] Figures of the different forms of this species are given in vol. i. of Edward’s “Butterflies of North America.”

[66] Only the species of _Smerinthus_ can be made to lay eggs regularly in confinement; _Macroglossa Stellatarum_ laid a number in a large gauze-covered breeding-cage; the species of _Deilephila_ could not be induced to lay more than single ones in such a cage. From species of _Chærocampa_ also I never obtained but a few eggs, and from _Sphinx_ and _Acherontia_ never more than single ones.

[67] [Eng. ed. Since the appearance of the German edition of this work, numerous descriptions of the young stages of caterpillars have been given, but in all cases without representing the relationship of the forms.] [In the excellent figures of larvæ at various stages of growth, given in some of the more recent works on Lepidoptera, there will be found much material which may be regarded as a contribution to the field of research entered on by the author in the present essay, _i.e._ the ontogeny and comparative morphology of larval markings, although it is much to be regretted that the figures and descriptions have not been given from this point of view. In his “Butterflies of North America,” for example, W. H. Edwards figures the young as well as the adult larvæ of species of _Apatura_, _Argynnis_, _Libythea_, _Phyciodes_, _Limenitis_, _Colias_, _Papilio_, &c. Burmeister, in his recently published “Lépidoptères de la République Argentine,” figures the young stages of species of _Caligo_, _Opsiphanes_, _Callidryas_, _Philampelus_, &c. Messrs. Hellins and Buckler have figured and described the early stages of large numbers of the caterpillars of British Lepidoptera, but their figures remain unpublished. The larvæ of many of our native species belonging to the genera _Liparis_, _Tæniocampa_, _Epunda_, _Cymatophora_, _Calocampa_, &c., are dull when young, but become brightly coloured at the last moult. Such changes of colour are probably associated with some change, either in the habits or in the environment; and a careful study of the ontogenetic development of such species in connection with their life-history would furnish results of great value to the present inquiry. The same remarks apply to those _Noctuæ_ larvæ which are brightly coloured in their young stages, and become dull when adult.

Among other papers which may be considered as contributions to the present subject, I may mention the following:--In 1864 Capt. Hutton published a paper, “On the Reversion and Restoration of the Silkworm, Part II.” (Trans. Ent. Soc. 1864, p. 295), in which he describes the various stages of development of several species of _Bombycidæ_. In 1867 G. Semper published accounts of the early stages of several Sphinx-larvæ (“Beiträge zur Entwicklungsgeschichte einiger ostasiatischer Schmetterlinge,” Verhandl. k.k. Zoolog.-botan. Gesell. in Wien, vol. xvii.). The question as to the number of claspers in young _Noctuæ_ larvæ has been raised in notes by Dr. F. Buchanan White (“Ent. Mo. Mag.,” vol. v. p. 204) and B. Lockyer (“Entomologist,” 1871, p. 433). A valuable paper, “On the Embryonic Larvæ of Butterflies,” was published in 1871 by S. H. Scudder (“Ent. Mo. Mag.,” vol. viii. p. 122). For remarks on the development of the larva of _Papilio Merope_, see J. P. Mansel Weale in Trans. Ent. Soc., 1874, p. 131, and Pl. I.; also this author on the young stages of the larva of _Gynanisa Isis_, Trans. Ent. Soc., 1878, p. 184. For an account of the development of the larvæ of certain North American species of _Satyrus_, see W. H. Edwards in the “Canadian Entom.,” vol. xii. p. 21. Mr. P. H. Gosse’s recent description of the newly hatched caterpillar of _Papilio Homerus_ (Proc. Ent. Soc. 1879, p. lv), furnishes a good illustration of the value of studying the ontogeny. The natural affinities of the _Papilionidæ_ were at one time much disputed, some systematists placing this family at the head of the Lepidoptera, and others regarding them as being more closely allied to the moths. Mr. Gosse’s observation tends to confirm the latter view, now generally received by Lepidopterists, since he states that the larva in question “suggests one of the great _Saturniadæ_, such as _Samia Cecropia_.” Mr. Scudder, in the paper above referred to, adopts an analogous argument to show the close relationship between the _Papilionidæ_ and _Hesperidæ_. R.M.]

[68] [Mr. A. G. Butler has recently furnished a good illustration of the danger of classifying Lepidoptera according to the affinities of the perfect insects only, in his paper, “On the Natural Affinities of the Lepidoptera hitherto referred to the Genus _Acronycta_ of authors,” Trans. Ent. Soc. 1879, p. 313. If the author’s views are ultimately accepted, the species at present grouped under this genus will be distributed among the _Arctiidæ_, _Liparidæ_, _Notodontidæ_, and _Noctuæ_. Mr. Butler’s determination of the affinities of the species supposed to belong to the genus mentioned, is based chiefly upon a comparative examination of the larvæ, and this is far more likely to show the true blood-relationship of the species than a comparison of the perfect insects only. A study of the comparative ontogeny can alone give a final answer to this question. R.M.]

[69] [In his recent revision of the _Sphingidæ_, Mr. A. G. Butler (Trans. Zoo. Soc., vol. ix. part x.) retains Walker’s arrangement. R.M.]

[70] The deposition of black pigment may commence immediately before ecdysis.

[71] [Mr. Herbert Goss states (Proc. Ent. Soc. 1878, p. v.) that according to his experience, the green and brown varieties of _C. Porcellus_ (erroneously printed as _Elpenor_ in the passage referred to) are about equally common, the former colour not being in any way confined to young larvæ. Mr. Owen Wilson in his recent work, “The Larvæ of British Lepidoptera and their food-plants,” figures (Pl. VIII., Figs. 3 and 3a) the two forms, both apparently in the adult state. During the years 1878-79, my friend, Mr. J. Evershed, jun., took five of these full-grown larvæ in Surrey, one of these being the green variety. In order to get more statistics on this subject, I applied this year (1880) to Messrs. Davis of Dartford, who informed me that among 18-20 adult caterpillars of _Porcellus_ in their possession, there was only one green specimen. R.M.]

[72] I unite the genera _Pergesa_ and _Darapsa_ of Walk. with _Chærocampa_, Dup.; the first appears to me to be quite untenable, since it is impossible that two species, of which the caterpillars agree so completely as those of _C. Elpenor_ and _Porcellus_, can be located in different genera. _Porcellus_ indeed was referred to the genus _Pergesa_ because of its different contour of wings, an instance which distinctly shows how dangerous it is to attempt to found Lepidopterous genera without considering the caterpillars. The genus _Darapsa_ also appears to me to be of very doubtful value, and in any case requires further confirmation with respect to the larval forms.

[73] [Mr. A. G. Butler (Trans. Zoo. Soc., vol. ix., part. x., 1876) gives a list of about eighty-four species of _Chærocampa_, and sixteen of _Pergesa_, besides numerous other species belonging to several genera placed between _Chærocampa_ and _Pergesa_. Of _Darapsa_, he states “that this genus was founded upon most heterogeneous material, the first three species being referable to Hübner’s genus _Otus_, the fifth to Walker’s genus _Diodosida_, the sixth and eighth to the genus _Daphnis_ of Hübner, the seventh, ninth, and tenth to _Chærocampa_ of Duponchel; there therefore remains only the fourth species, allied to _Chærocampa_, but apparently sufficiently distinct.” The species still retained in the genus _Darapsa_ is _D. rhodocera_, Wlk., from Haiti. R.M.]

[74] [_Otus Syriacus_ of Butler’s revision. R.M.]

[75] Abbot and Smith. “The Natural History of the rarer Lepidopterous Insects of Georgia, collected from the observations of John Abbot, with the plants on which they feed.” London, 1797, 2 vols. fol.

[76] [_Otus Chœrilus_ and _O. Myron_ of Butler’s revision. R.M.]

[77] [To this group may also be added _Ampelophaga Rubiginosa_, Ménétriés, from China and Japan, the caterpillar of which, having the distinct subdorsal line without any trace of eye-spots, is figured by Butler (_loc. cit._, Pl. XCI., Fig. 4). This author also gives a figure of another species belonging to the subfamily _Chærocampinæ_ (Pl. XC., Fig. 11), viz. _Acosmeryx Anceus_, Cram., from Amboina, Java, Silhet, and S. India; the caterpillar is green, with seven oblique yellow stripes along the sides, and a very conspicuous white subdorsal line with a red border above. As there are no eye-spots, this species may be referred to the present group provisionally, although its general marking is very distinct from that of the _Chærocampa_ group. R.M.]

[78] [Eng. ed. Dr. Staudinger has since obtained the caterpillar of _C. Alecto_ from Beyrout; it possesses “a very distinct subdorsal line, and on the fourth segment a beautiful eye-spot, which is repeated with gradual diminution to segments 7-8”.]

[79] Figured in “A Catalogue of Lepidopterous Insects in the Museum of the East India Company,” by Thomas Horsfield and Frederick Moore. London, 1857. Vol. i., Pl. XI.

[80] Figured in Trans. Ent. Soc., New Series, vol. iv., Pl. XIII.

[81] _Ibid._

[82] [The following species figured by Butler (_loc. cit._ Pls. XC. and XCI.) appear to belong to the second group--_Chærocampa Japonica_, Boisd., which is figured in two forms, one brown, and the other green. The former has two distinct ocelli on the fourth and fifth segments, and a distinct rudiment on the sixth, whilst the subdorsal line extends from the second eye-spot to the caudal horn, and beneath this line the oblique lateral stripes stand out conspicuously in dark brown on a lighter ground. The ocelli are equally well developed on the fourth and fifth segments in the green variety, the subdorsal line commencing on the sixth segment, and extending to the caudal horn; there is no trace of a third eye-spot, nor are there any oblique lateral stripes; the insect is almost the exact counterpart of _C. Elpenor_ in its fourth stage. (See Fig. 21, Pl. IV.) _Pergesa Mongoliana_, Butl., is brown, without a trace of the subdorsal line except on the three front segments, and with only one large eye-spot on the fourth segment. _Chærocampa Lewisii_, Butl., from Japan, is likewise figured in two forms. The brown variety has the subdorsal line on the three front segments only, distinct ocelli on the fourth and fifth segments, and gradually diminishing rudiments on the remaining segments. The green form appears to be transitional between the present and the third group, as it possesses a distinct, but rudimentary eye-spot on the third segment, besides the fully developed ones on the fourth and fifth, and very conspicuous, but gradually decreasing repetitions of rudimentary ocelli on segments 6-10. To this group may be added _Chærocampa Aristor_, Boisd., the caterpillar of which is figured by Burmeister (Lép. Rép. Arg., Pl. XV., Fig. 4) in the characteristic attitude of alarm, with the front segments retracted, and the ocelli on the fourth segment prominently exposed. The subdorsal line is present in this species. Burmeister also figures two of the early stages (Pl. XV., Fig. 7, A and B), and describes the complete development of _Philampelus Labruscæ_, another species belonging to the subfamily _Chærocampinæ_. The earliest stage (3-4 days old) is simple green, with no trace of any marking except a black spot on each side of the fourth segment, the position of the future ocelli. A curved horn is present both in this stage and the following one, during which the caterpillar is still green, but now has seven oblique red lateral stripes. The caudal horn is shed at the second moult, after which the colour becomes darker, the adult larva (figured by Madame Mérian, in her work on Surinam, pl. 34 and Sepp., pl. 32) being mottled brown. In addition to the ocellus on the fourth segment, there is another slightly larger on the eleventh segment, so that this species may perhaps be another transition to the third group; but our knowledge is still too imperfect to attempt to generalize with safety. R.M.]

[83] Cat. Lep. Ins. East Ind. Comp., Pl. XIII. [Figured also by Butler (=_Chæerocampa Silhetensis_, Walker), _loc. cit._ Pl. XCII., Fig. 8. R.M.]

[84] Cat. Lep. Ins. East Ind. Comp., Pl. XIII. [Figured also by Butler, _loc. cit._ Pl. XCI., Fig. 1. R.M.]

[85] Horsfield and Moore, _loc. cit._ Pl. X.

[86] _Ibid._ [=_Pergesa Acteus_, Walker. R.M.]

[87] [Figured also by Burmeister, _loc. cit._ Pl. XV., Fig. 3. R.M.]

[88] Horsfield and Moore, _loc. cit._, Pl. XI.

[89] To be accurate this should be designated the infra-spiracular line; but this term cannot be well applied except in cases where there is also a supra-spiracular line, as, for instance, in _Anceryx (Hyloicus) Pinastri_.

[90] Upon this fact obviously depends the statement of that extremely accurate observer Rösel, that the caterpillar of _Euphorbiæ_ is but very slightly variable (“Insektenbelustigungen,” Bd. iii. p. 36). I formerly held the same opinion, till I convinced myself that this species is very constant in some localities, but very variable in others. It appears that local influences make the caterpillar variable.

[91] The green is considerably too light in Fig. 45.

[92] “Die Pflanzen und Raupen Deutschlands.” Berlin, 1860, p. 83.

[93] Fig. 62, Pl. VII., is copied from Boisduval.

[94] The fading of the red anteriorly has not been represented in the figure.

[95] [The caterpillar of _Deilephila Euphorbiarum_, figured by Burmeister (Lép. Rép. Arg., Pl. XVI, Fig. 1) belongs to this stage. R.M.]

[96] [In concluding this account of the _Chærocampinæ_ I may call attention to the following species, which have since been figured by Burmeister:--_Pachylia Ficus_, Linn. (_loc. cit._ Pl. XIV., Figs. 1 and 2); during the three first stages the larva is uniformly green, with a yellow subdorsal line, and below this ten oblique yellow stripes slanting away from the head; after the third moult the colour completely changes, the whole area of the body being divided into two distinct portions by the subdorsal line, above which the colour is red, and underneath of a pale green; the oblique stripes have almost disappeared; no occelli nor annuli are present. _Pachylia Syces_, Hübn. (_loc. cit._ Fig. 3); very similar to the last species in its young stages (figured also by Mérian, Surin. pl. 33). _Philampelus Vitis_, Linn. (_loc. cit._ Figs. 4 and 5); two stages represented; between first and second moults green, with oblique paler stripes slanting in same direction as in _Pachylia_, and each one containing a red streak surrounding the spiracle. When adult, the ground-colour is yellow above and green beneath, the whole surface being mottled with deep black and red transverse markings; the oblique stripes whitish, bordered with black at their lower extremities (figured also by Mérian, pls. 9 and 39). _Philampelus Anchemolus_, Cram. (_loc. cit._ Pl. XV., Fig. 1; Mérian, pl. 47); green when young, with seven oblique red stripes; when adult, uniformly brown, with seven pale yellow lateral markings, the first four of which are spots, and the remainder broad oblique stripes slanting forwards. _Philampelus Labruscæ_, (see note 82, p. 195). R.M.]

[97] [_Mimas Tiliæ_ of Butler’s revision. The author states that this genus is “easily distinguished from _Laothoë_ by the form of the wings, the outer margin of secondaries deeply excavated below the apex, and the secondaries narrow and not denticulated.” Here again we have a clashing of the results arrived at by a study of the ontogeny of the larvæ, on the one hand, and the founding of genera on the characters of the imagines only, on the other. Of the three species discussed by Dr. Weismann, Mr. Butler, following other authors, refers _Tiliæ_ to the genus _Mimas_, _Populi_ to _Laothoë_, and _Ocellatus_ to _Smerinthus_. It is to be hoped that when our knowledge of the developmental history of larvæ is more complete in all groups, a reconciliation between the results of the biological investigator and the pure systematist will be brought about, so that a genus may not, as at present, have such very different values when regarded from these two points of view. R.M.]

[98] The caterpillar is thus figured by Rösel.

[99] [In 1879 Mr. E. Boscher found about thirty full-grown caterpillars of this species in the neighbourhood of Twickenham, ten to twelve of which were feeding on _Salix viminalis_, and the remainder, from a locality not far distant, on _Salix triandra_. The whole of the specimens taken on the plant first named, had the red-brown spots above and below the oblique stripes more or less completely developed, as I myself had an opportunity of observing. In these spotted specimens the ground-colour was bright yellowish-green, and in the others this colour was dull whitish-green above, passing into bluish-green below. Should these observations receive wider confirmation, it would be fair to conclude that this species is now in two states of phyletic development, the more advanced stage being represented by the brighter spotted variety. (See also Proc. Ent. Soc. 1879, p. xliv.). Mr. Peter Cameron has recently suggested (Trans. Ent. Soc. 1880, p. 69) that the reddish-brown spots on the _Smerinthus_ caterpillars may serve for purposes of disguise, as they closely resemble, both in colour and form, certain galls (_Phytoptus_) of the food-plants of these species. If this view be admitted, these spots must be considered as a new character, now being developed by natural selection. The variation in the ground-colour of the two forms of _S. Ocellatus_ may possibly be phytophagic, but this can only be decisively settled by a series of carefully conducted experiments. R.M.]

[100] “Insekten-Belustigungen,” Suppl. Pl. 38, Fig. 40.

[101] “Catalogue of Lepidop.” British Museum. [Butler divides the subfamily _Smerinthinæ_ into 17 genera, containing 79 species, viz. _Metamimas_, 2; _Mimas_, 4; _Polyptychus_, 7; _Lophostethus_, 1; _Sphingonæpiopsis_, 1; _Langia_, 2; _Triptogon_, 23; _Laothoë_, 2; _Cressonia_, 3; _Paonias_, 2; _Calasymbolus_, 5; _Smerinthus_, 5; _Pseudosmerinthus_, 2; _Daphnusa_, 4; _Leucophlebia_, 5; _Basiana_, 10; _Cæquosa_, 1. R.M.]

[102] “Cabinet Orient. Entom.,” p. 13, Pl. VI., Fig. 2. [Butler places this species doubtfully among the _Sphinginæ_. R.M.]

[103] “Catalogue of the Lepidop. Insects of the E.I. Co.,” by Horsfield and Moore. Pl. VIII., Fig. 6.

[104] [The larvæ of four other species of this subfamily have since been made known through Mr. Butler’s figures. _Smerinthus Tatarinovii_, Ménetriés (_loc. cit._ Pl. XC., Fig. 16), from Japan, is “pale sea-green, tuberculated with white, with seven lateral, oblique, crimson-edged white stripes.” There is no trace of the subdorsal line shown in the figure, so that this species thus appears to be in the third phyletic stage of development. _Smerinthus Planus_, Walker, from China (_loc. cit._ Pl XCII., Fig. 11), is “pale green, with white or yellow lateral stripes.” A trace of the subdorsal line remains on the front segments, thus showing that the species is in the second phyletic stage of development. _Triptogon Roseipennis_, Butler, from Hakodadi (_loc. cit._ Pl. XCI., Fig. 6), is represented as yellow, with seven oblique white stripes, with large irregular triangular red spots extending from the anterior edge of the stripes, nearly across each segment. It is probably in the third phyletic stage. The Indian _Polyptychus Dentatus_, Cramer (_loc. cit._ Pl. XCI., Fig. 10), is “bluish-green at the sides, with oblique purple stripes, with a broad, dorsal, longitudinal, golden-green band, bordered by subtriangular purple spots, one above each stripe.” The dorsal band is bordered by coloured stripes, which may be the subdorsal lines; but the position in which it is figured, and its very different mode of coloration, make it very difficult to compare satisfactorily with the foregoing species. The genus _Ambulyx_ is closely allied to the _Smerinthinæ_, and the two following species may be here mentioned: _A. Gannascus_, Stoll, figured by Burmeister (_loc. cit._ Pl. XIII., Fig. 5), is green, with a yellow subdorsal line, and seven oblique white lateral stripes, edged with red. _A. Liturata_, Butl. (_loc. cit._ Pl. XCI., Fig. 2), is yellowish-green above, passing into bluish-green below. The subdorsal is present on the three front segments, and is followed by a row of white, elongated patches, one on each segment, these being the upper portions of a row of lateral oblique stripes. The thickened upper extremities of the latter are edged with red, and their arrangement is very suggestive of their having arisen from the breaking up of a subdorsal line. R.M.]

[105] [Butler catalogues 43 species of this genus. R.M.]

[106] The deposition of eggs was accomplished by the insect laying hold of the point of a twig with its legs during flight, and curving its abdomen upwards against a leaf, the wings being kept vibrating. The egg is instantaneously fastened to the leaf. This operation is repeated from twice to four times successively, the moth then hovering over and sucking at the flowers for some time. The eggs exactly resemble in colour the young green buds of _Galium_.

[107] [Figures of a remarkable case of gynandromorphism in a butterfly (_Cirrochroa Aoris_, Doubl.) have recently been published by Prof. Westwood (Trans. Ent. Soc. 1880, p. 113). On the right fore- and hind-wings of a male specimen there are patches of female colouring, thus bearing out in a very striking manner the above views concerning the non-fusibility of characters (in this case sexual) which have been long fixed. Complete (_i.e._ half-and-half) gynandromorphism is not uncommon in butterflies. R.M.]