Chapter XIV: Introduction (2)

[108] [I have long held the opinion that the di- and trimorphism displayed by certain butterflies has originated through polymorphism from ordinary variability. I will not here enter into details, but will only cite a few instances indicating the general direction of the arguments. The phenomenon to which I refer is that so ably treated of by Mr. A. R. Wallace (see Part I., p. 32, note 20) and others. One male has often two or more distinctly coloured females, and in such cases one form of the female generally resembles the male in colour. Cases of polymorphic _mimetic_ females may for the present be excluded, in order to reduce the argument to its greatest simplicity. Thus, in the case of native species, _Colias Edusa_ has two females, one having the orange ground-colour of the male, and the other the well-known light form, var. _Helice_. So, also, _Argynnis Paphia_ has a normal female and the dark melanic form var. _Valezina_. Numerous other cases might be mentioned among exotic species; and, looking at the phenomenon as a whole, it is seen to be one of _gradation_. For instance, our common “Blues” (_Plebeius Icarus_, _P. Thetis_, &c.) have females showing a complete gradation between the ordinary blue male and the brown female coloration. In a large number of specimens of _Callosune Eupompe_ in my cabinet, collected in Arabia by the late J. K. Lord, there is a completely graduated series of females, varying from individuals having the scarlet tips of the fore-wings as strongly developed as in the males, to specimens without a trace of such colouring; and the same is the case with other species of this and allied genera. In such instances it is only necessary for the intermediate female forms to become extinct, in order to have true cases of dimorphism. It is significant that in 1877, when _Colias Edusa_ appeared in this country in such extraordinary profusion, large numbers of _intermediate forms_ were captured, these forming an uninterrupted series connecting the normal female and the var. _Helice_. R.M.]

[109] [Many of our best describers of caterpillars, such as the late Edward Newman, Messrs. Hellins and Buckler, &c., have described the various forms of numerous polymorphic species, but not from the point of view of the comparative morphology and ontogeny of the markings. R.M.]

[110] [In Butler’s revision both these species are placed in the genus _Hemaris_. R.M.]

[111] [This species is figured also by Butler (_loc. cit._ Pl. XC., Fig. 9), who represents it with seven oblique green lines between the spiracles and below the subdorsal line. R.M.]

[112] “Cat. E. Ind. Co. Mus.,” Pl. VIII., Fig. 2. [Walker, Lepidop. Heter. VIII., p. 92, No. 14, 1856; this species is strictly confined to Java. R.M.]

[113] [Eng. ed. The caterpillar is described and figured by Millière, “Iconographie des Chenilles et Lépidoptères inédits,” tome iii., Paris, 1869; also in the Annales, Soc. Linn. de Lyon, 1871 and 1873.] [This sp. = _Hemaris Croatica_, Esper., of Butler’s revision. R.M.]

[114] [The following additional species of the subfamily _Macroglossinæ_ have been figured by Butler:--_Lophura Hyas_, Walk. (_loc. cit._ Pl. XC., Figs. 1 and 2), Hong-Kong, Silhet, and Java. The larva is apparently figured in two stages, the younger being red-brown with oblique white stripes, and the head and three front segments green. The larger specimen is green, mottled with red-brown, and no oblique stripes. In both figures the subdorsal line is indicated. The whole colouring is very suggestive of protective resemblance. _Hemaris Hylas_, Linn., from China, Japan, Ceylon, India, Australia, and Africa (_loc. cit._ Pl. XC., Fig. 4). The upper part of the body is light blue, and the lower part green, the two areas being separated by a white subdorsal line bordered above with brown. The dorsal line is feebly represented. _Macroglossa Belis_, Cram., N. India (_loc. cit._ Pl. XC., Fig. 6), is figured with the ground-colour deep indigo; a conspicuous white subdorsal, and a yellow spiracular line is present; on the side of each segment, between the two lines mentioned, there is a large red spot with a yellow nucleus (? eye-spots), the spots decreasing in size towards the head and tail; these probably confer upon this species some special protective advantage. _Macroglossa Pyrrhosticta_, Butler, China and Japan (_loc. cit._ Pl. XC., Fig. 8), is greenish-white with dorsal and subdorsal lines, and seven dark oblique stripes along the sides, below the subdorsal line. Of the foregoing species _Hemaris Hyas_ appears to be in the same phyletic stage as _M. Stellatarum_ and _M. Croatica_, &c., whilst _M. Pyrrhosticta_ is probably, together with _M. Corythus_ and _M. Gilia_, in another and more advanced stage, which is also passed through by _Lophura Hyas_ in the course of its ontogenetic development. This last species (adult) and _M. Belis_ may represent phyletic stages still further advanced. _Caliomma Pluto_, Walk., of which the caterpillar is figured by Burmeister (_loc. cit._ Pl. XIII., Fig. 1), appears to be a case of special protective resemblance to a twig or branch of its food-plant. Figured also by Chavannes; Bull. Soc. Vadoise des Sci. Nat., Dec. 6th 1854. R.M.]

[115] [Genus _Pterogon_, Boisd., = _Proserpinus_ and _Lophura_ (part). Butler, _loc. cit._ p. 632. The species above treated of = _Proserpinus Œnotheræ_, Fabr. R.M.]

[116] [These species = _Thyreus Abboti_ and _Proserpinus Gauræ_ of Butler’s revision. Of the former he states:--“Transformations described, and larva and imago figured, Am. Ent. ii. p. 123, 1870; the larva is also figured by Scudder in Harris’s ‘Correspondence,’ Pl. III., Fig. 1 (1869), and by Packard in his ‘Guide,’ p. 276, Fig. 203.” R.M.]

[117] [_Proserpinus (Sphinx) Gorgon_, Esp. R.M.]

[118] Rösel, _loc. cit._ vol. iii., p. 26, note.

[119] Figured and described by Abbot and Smith. [_Macrosila (Sphinx) Cingulata_ is figured also by Burmeister, _loc. cit._ Pl. XII., Fig. 1. R.M.]

[120] Figured in “Cat. Lep. E. Ind. Co.”

[121] See the figure in Sepp’s Surinam Lepidoptera, P. 3, Pl. CI., 1848. A specimen in alcohol of the adult caterpillar is in the Berlin Museum. [The following is the synonymy of the above mentioned species:--_Macrosila Hasdrubal_, Walk. = _Pseudosphinx (Sphinx) Tetrio_, Linn.; _M. Cingulata_ = _Protoparce (Sphinx) Cingulata_, Fabr.; _M. Rustica_ = _Protoparce (Sphinx) Rustica_, Fabr.; _Sphinx Convolvuli_, Linn. = _Protoparce Convolvuli_; _S. Carolina_, Linn. = _P. Carolina_; the other species remain in the genera, as given above. The following additional species of _Sphinginæ_ and _Acherontiinæ_ have been figured by Butler:--_Pseudosphinx Cyrtolophia_, Butl., from Madras (_loc. cit._ Pl. XCI., Figs. 11 and 13); _Protoparce Orientalis_, Butl., from India, China, Java, &c. (Pl. XCI., Fig. 16); _Diludia Vates_, Butl. from India, &c. (Pl. XCI., Fig. 18); _Nephele Hespera_, Fabr., from India, Australia, &c. (Pl. XCI., Fig. 20); _Acherontia Morta_, Hübn., from Java, China, India, &c. (Pl. XCII., Fig. 9); and _A. Medusa_, Butl., from nearly the same localities as the last (Pl. XCII., Fig. 10). Most of these species fall under Dr. Weismann’s general remarks, so that it is unnecessary to give detailed descriptions. The most divergent marking is that of _P. Cyrtolophia_, which has a broad white dorsal line bordered with pink, and two large pink ovals on the back of the four anterior segments, the hindmost and larger of these being bisected by the dorsal line. In _N. Hespera_ the subdorsal line is present on segments 6 to 11 only, and it is highly significant that the oblique stripes are absent from these segments, but are present on the anterior segments, where the subdorsal line fails. With reference to the larva of _A. Atropos_, Mr. Mansel Weale states (Proc. Ent. Soc. 1878, p. v.) that in S. Africa the ordinary form feeds generally on _Solanaceæ_, whilst the darker and rarer variety is found only on species of _Lantana_. The following species of these subfamilies are figured by Burmeister: _Amphonyx Jatrophæ_ (_loc. cit._ Pl. XI., Fig. 1); _Protoparce (Diludia) Florestan_, Cram. (Fig. 2); _Sphinx Justiciæ_, Walk. (Fig. 3); _Protoparce (Diludia) Lichenea_, Walk. (Fig. 4); _Sphinx (Protoparce) Cingulata_, Fabr. (Pl. XII., Fig. 1); and _Sphinx Cestri_ (Fig. 5). All these species have the characteristic Sphinx-like markings. _Dilophonota Ello_, Linn. (Pl. XII., Fig. 2), is greenish-brown with a yellow subdorsal line, and _D. Hippothöon_ (Fig. 4), yellow with a whitish subdorsal. Neither of these has oblique stripes. _D. Œnotrus_, Cram. (Fig. 3), has neither stripes nor subdorsal, but is uniform brown above, passing into green beneath. _Protoparce Albiplaga_, Walk. (Pl. XIII., Fig. 2, also Mérian, Pl. III., and Abbot and Smith, I., Pl. XXIV.), pale green with large yellow, black-bordered patches surrounding the spiracles. _Pseudosphinx Tetrio_, Linn. (Pl. XIII., Fig. 3), and _P. Scyron_ (Fig. 4) are black with broad transverse belts, yellow and white respectively, encircling the middle of each segment. These light bands serve very effectively to break up the uniform surface of the large bodies of these insects, but the whole marking is suggestive of distastefulness. R.M.]

[122] [The species referred to is placed by Butler in Hübner’s genus _Hyloicus_. R.M.]

[123] [= _Ellema Coniferarum_, of Butler’s revision. R.M.]

[124] [= _Dilophonota Ello_ of Butler’s revision. R.M.]

[125] “Synopsis of the North American Sphingides.” Philadelphia, 1859.

[126] [The larvæ of many moths which feed on deciduous trees during the autumn and hibernate, are stated to feed on low-growing plants in the spring, before the buds of their food-trees open. On the other hand, low-plant feeders, such as _Triphæna Fimbria_, &c., are stated to sometimes feed at night in early spring on the buds of trees. The habits and ontogeny of these species are of special interest in connection with the present researches, and are well worthy of investigation. R.M.]

[127] “Neuer Beitrag zum geologischen Beweise der Darwin’schen Theorie.” 1873, Nos. 1 and 2. [This principle, in common with many others which have only been completely worked out of late years, is foreshadowed by Darwin. Thus, he states when speaking of inheritance at corresponding periods of life: “I could give a good many cases of variations (taking the word in the largest sense) which have supervened at an earlier age in the child than in the parent” (“Origin of Species,” 1st ed., 1860, p. 444). In the case of inherited diseases also: “It is impossible to ... doubt that there is a strong tendency to inheritance in disease at corresponding periods of life. When the rule fails, the disease is apt to come on earlier in the child than in the parent; the exceptions in the other direction being very much rarer.” (“Variation of Animals and Plants under Domestication,” 1st ed., 1868, vol. ii., p. 83.) R.M.]

[128] [If the reddish-brown spots on the larva of _S. Populi_ have the protective function assigned to them by Mr. Peter Cameron (Trans. Ent. Soc. 1880, p. 69), it can be readily understood that they would be of service to the insect in the fourth stage, and the backward transference of this character might thus be accelerated by natural selection, in accordance with the above principles. (See, also, note 100, p. 241.) R.M.]

[129] [For cases of correlation of habit with protective resemblance in larvæ, see a paper in “Ann. and Mag. of Nat. Hist.,” Feb., 1878, pp. 159, 160. Also Fritz Müller on a Brazilian Cochliopod larva, Trans. Ent. Soc. 1878, p. 223. Mr. Mansel Weale states, with reference to S. African _Sphingidæ_ (Proc. Ent. Soc. 1878, p. vi.), that many species when seized “have a habit of doubling up the body, and then jumping a considerable distance with a spring-like action. This is especially the case with species having eye-like markings; and it is probable that if attacked by birds in a hesitating manner, such species might effect their escape amid the grass or foliage.” Many of the defensive weapons and habits of larvæ are doubtless means of protection from ichneumons and other parasitic foes. In the case of saw-flies, Mr. Peter Cameron has shown (Trans. Ent. Soc. 1878, p. 196) that the lashing about of the posterior part of the body may actually frighten away such enemies. The grotesque attitude and spider-like appearance and movements of the caterpillar of _Stauropus Fagi_ are considered by Hermann Müller (“Kosmos,” Nov., 1879, p. 123) to be means of protection from ichneumons. Among the most remarkable means of defence possessed by larvæ is that of secreting a liquid, which Mr. W. H. Edwards has shown, in the case of certain North American _Lycænidæ_ (“Canadian Entomologist.” vol. x., 1878, pp. 3-9 and 131-136), to be attractive to ants, who regularly attend these caterpillars, in the same manner and for the same purpose as they do our aphides. The mutual advantage derived by the ants and larvæ was discovered in the case of _Lycæna Pseudargiolus_. Mr. Edwards states that the _mature_ larva of this species is singularly free from Hymenopterous and Dipterous parasites:--“Why this species, and doubtless many other _Lycænæ_, are thus favoured will, perhaps, in some degree appear from a little incident to be related. On 20th June, in the woods, I saw a mature larva on its food-plant; and on its back, facing towards the tail of the larva, stood motionless one of the larger ants.... At less than two inches behind the larva, on the stem, was a large ichneumon-fly, watching its chance to thrust its ovipositor into the larva. I bent down the stem, and held it horizontally before me, without alarming either of the parties. The fly crawled a little nearer and rested, and again nearer, the ant making no sign. At length, after several advances, the fly turned its abdomen under and forward, thrust out its ovipositor, and strained itself to the utmost to reach its prey. The sting was just about to touch the extreme end of the larva, when the ant made a dash at the fly, which flew away, and so long as I watched--at least five minutes--did not return. The larva had been quiet all this time, its tubes out of sight, and head buried in a flower-bud, but the moment the ant rushed and the fly fled, it seemed to become aware of the danger, and thrashed about the end of its body repeatedly in great alarm. But the tubes were not protruded, as I was clearly able to see with my lens. The ant saved the larva, and it is probable that ichneumons would in no case get an opportunity to sting so long as such vigilant guards were about. It strikes me that the larvæ know their protectors, and are able and willing to reward them. The advantage is mutual, and the association is friendly always.” Those who are familiar with Mr. Belt’s description of the standing armies of ants kept by the “bull’s-horn thorn” (“Naturalist in Nicaragua,” pp. 218-222) and by certain _Cecropiæ_ and _Melastomæ_, will be struck with the analogy between these and the foregoing case. R.M.]

[130] [The adaptive resemblance is considerably enhanced in _Catocala_ and in _Lasiocampa Quercifolia_ by the row of fleshy protuberances along the sides of these caterpillars, which enables them to rest on the tree trunks by day without casting a sharp shadow. The hairs along the sides of the caterpillar of _Pæcilocampa Populi_ doubtless serve the same purpose. (See a paper by Sir John Lubbock, Trans. Ent. Soc. 1878, p. 242; also Peter Cameron, _ibid._, 1880, p. 75.) It is well known to collectors that one of the best methods of finding the caterpillars of the _Catocalæ_ is to _feel_ for them by day on the barks of their respective food-trees, or to beat for them at night. R.M.]

[131] [See Wallace’s “Contributions to the Theory of Natural Selection,” 1st ed., p. 62. Also a paper in “Ann. Mag. Nat. Hist.” Feb. 1878, p. 159, for cases in point. Rösel in 1746 mentioned this habit in _Calocampa Exoleta_. Hermann Müller has recorded many other similar instances on the authority of Dr. Speyer; see “Kosmos,” Nov., 1879, p. 114. R.M.]

[132] [Andrew Murray called attention to this fact in 1859 (“Edinburgh New Philos. Journ.,” Jan., 1860, p. 9). This view is also corroborated by the fact that no internal feeders are green; see note 142, p. 310 and Proc. Zoo. Soc. 1873, p. 159. R.M.]

[133] [Proc. Ent. Soc. March 4th, 1867; and “Contributions to the Theory of Natural Selection,” 1st ed., pp. 117-122; also Darwin’s “Descent of Man,” 2nd ed., p. 325. Among the most important recent additions to the subject of the colours, spines, and odours of caterpillars, I may call attention to a paper by Fritz Müller (“Kosmos,” Dec., 1877), the following abstract of which I communicated to the Entomological Society (Proc. 1878, pp. vi, vii):--“The larvæ of _Dione Juno_ and _Acræa Thalia_ live gregariously, and are brown in colour; they are covered with spines, but, being of dull colours, their spiny protection (which in the case of _D. Juno_ is very imperfect) would not preserve them unless they were distinguished as inedible at the right time, and not after being seized, in accordance with the principles laid down by Mr. Wallace. It is suggested that the social habits of the larvæ which lead then to congregate in large numbers, make up for their want of colour, since their offensive odour then gives timely warning to an approaching enemy. The caterpillars of _Colænis Julia_ and _Dione Vanillæ_ are equally wanting in bright colours, but are solitary in their habits, and these species rest on the under side of the leaf when feeding. On the other hand, the caterpillars of _Heliconius Eucrate_, _Colænis Dido_, and _C. Isabella_, which are of solitary habits, and which freely expose themselves, are very gaudily coloured, and therefore most conspicuous. As examples of nearly allied larvæ, of which some species are gregarious and others solitary, Fritz Müller mentions _Morpho_ and _Brassolis_, which are gregarious; while _Opsiphanes_ and _Caligo_ are solitary. The larva of _Papilio Pompeius_ also is gregarious, and those of _P. Nephalion_, _P. Polydamas_, and _P. Thoas_ are solitary.... Fritz Müller sums up his observations by remarking that those caterpillars which live alone, and lack the bright colouring as a sign of offensiveness, must hide themselves; as those of _C. Julia_ and _D. Vanillæ_. The spiny covering is much less a protection against birds than against smaller enemies; and they may, by the protective habit of living together, diffuse around themselves an offensive atmosphere, even to man, and thus gradually becoming shorter (as with _D. Juno_), the spines of these caterpillars become useless, and finally are altogether dropped.” See also Sir John Lubbock’s “Note on the Colours of British Caterpillars,” Trans. Ent. Soc. 1878, p. 239. Mr. Peter Cameron finds (Trans. Ent. Soc. 1880, pp. 71 and 75) that these remarks are also applicable to the larvæ of certain saw-flies. In 1877 Mr. J. W. Slater published a paper “On the Food of gaily-coloured Caterpillars” (Trans. Ent. Soc. 1877, p. 205), in which he suggested that such caterpillars might derive their distasteful qualities from feeding on plants containing poisonous or otherwise noxious principles. A much larger number of observations will be required, however, before this view can be accepted as of general application. A beautiful illustration of the theory of warning colours is given by Belt in his “Naturalist in Nicaragua,” p. 321. All the frogs found in the woods round St. Domingo are, with one exception, protectively coloured; they are of nocturnal habits, and are devoured by snakes and birds. The exception was a species of bright red and blue colours, which hopped about by day and made no attempt at concealment. From these facts Mr. Belt concluded that this species was inedible, and on trying the experiment with ducks and fowls this was found to be the case. R.M.]

[134] See the essay “Über den Einfluss der Isolirung auf die Artbilding.” Leipzig, 1872, p. 22.

[135] [See also preceding note 133, p. 294. R.M.]

[136] [Eng. ed. The habit of hiding by day occurs also in those caterpillars which resemble the bark of their food-trees. Thus _Catocala Sponsa_ and _Promissa_ conceal themselves by day in crevices of the bark, and are, under these circumstances, only found with difficulty. Dr. Fritz Müller also writes to me that in Brazil the caterpillars of _Papilio Evander_ rest in this manner in large numbers, crowded together into dense masses, on the trunks of the orange-trees, which they resemble in colour.]

[137] “Über den Einfluss der Isolirung auf die Artbildung.” Leipzig, 1872, p. 21.

[138] I am unfortunately not able to give exact numbers showing the relative proportions of the different forms, since I have never bred _S. Convolvuli_ from eggs, nor _C. Elpenor_ in sufficient numbers.

[139] [With reference to _C. Porcellus_, see note 71, p. 188. R.M.]

[140] [In the class of cases treated of in the foregoing portions of this essay, the external conditions remain unaltered during the lifetime of the caterpillar, but change of habit, and in some cases of colour, occurs when the insect has attained a size conceivable _à priori_, and are realized by observation, in which the environment itself may undergo change during the lifetime of the individual caterpillar. Thus, in the case of hibernating species, the colour which is adaptive to the autumnal colours of the foliage of their food-trees would not assimilate to that of the newly-opened leaves in the spring. I have already quoted (Proc. Zoo. Soc. 1873, p. 155) as instances of what may be called “seasonal adaptation,” the larvæ of _Geometra Papilionaria_, _Acidalia Degenararia_, and _Gnophos Obscurata_, and many more could be named. These species undergo a change of colour before or after hibernation, the change being always adaptive to the environment.

It has long been known that caterpillars which feed on flowers or on plants of variously-coloured foliage, in some cases partake of the colour of their food. See, for instance, Dr. L. Möller’s memoir, “Die Abhängigkeit der Inseckten von ihrer Umgebung,” 1867, and B. D. Walsh “On Phytophagic Varieties and Phytophagic Species,” Proc. Ent. Soc. Philadelph., vol. iii., p. 403. In 1865 Mr. R. McLachlan published a paper entitled “Observations on some remarkable varieties of _Sterrha Sacraria_, Linn., with general notes on variation in Lepidoptera” (Trans. Ent. Soc. 1865, p. 453), in which he gave many illustrations of this phenomenon. The larva of _Heliothis Peltiger_, according to Mr. Reading’s description (Newman’s “British Moths,” p. 438), is another case in point. In 1874 a number of instances were published by Mr. Thomas G. Gentry in a paper entitled “Remarkable Variations in Coloration, Ornamentation, &c., of certain Crepuscular and Nocturnal Lepidopterous Larvæ” (“Canadian Entomologist,” vol. vi., p. 85. See also W. H. Edwards’ description of the summer and autumnal larvæ of _Lycæna Pseudargiolus_; _Ibid._, vol. x., pp. 12, 13).

The caterpillars of the _Sphingidæ_ appear also in some cases to vary in a manner very suggestive of phytophagic influences. The observations upon _S. Ocellatus_ recorded in the previous note (p. 241) may perhaps be interpreted in this sense. In order to get experimental evidence upon this subject, I may add that Mr. E. Boscher was good enough at my request to repeat his observations, and conduct some breeding experiments during the present year (1880). In the same locality as that previously mentioned, seven larvæ were found feeding on _Salix viminalis_, all of which were the bright green spotted variety; and in the same osier-bed six more were found on another species of _Salix_, two of these being the bluish-green variety, and the other four the bright green form. Unless we have here a local race, these observations, in connection with those of last year, tend to show that the light green form is associated with _Salix viminalis_. When found in the natural state feeding on apple, the caterpillar of this species is generally, perhaps invariably, the bluish-green form. In order to try the effect of breeding the larvæ _ab ovo_ on distinct food-plants, a large number of eggs laid by a female _Ocellatus_ in July were divided into three batches, one being supplied with _Salix triandra_, another with _S. viminalis_, and the third lot with apple. The experiment unfortunately failed in great part, owing to most of the larvæ dying off, three from the third lot only surviving; but these were all of the bluish-green form, which colour was shown by all the caterpillars of this batch from their earliest stage. The observation is thus so far successful, as it goes to support the view that the variety mentioned is associated with apple (and _S. triandra?_) My friend Mr. W. J. Argent informs me that he had a number of specimens of _Sphinx Ligustri_ in his possession this autumn, some of which had been found on lilac and others on laurestinus, and he states that all those on the latter plant had the ground-colour distinctly darker than in those feeding on lilac. I learn also from Mr. W. Davis, of Dartford, that he found a number of these larvæ this year feeding on ash, and that they were all differently coloured to those found on lilac or privet, being of a more greyish-green. Another case of colour-variation in larvæ is that _Emmelesia Unifasciata_, specimens of which I have recently had an opportunity of examining, through the courtesy of Mr. W. Davis. This species feeds on the seeds of a species of _Bartsia_ when the capsules are in various stages of growth, and (omitting details of marking) those caterpillars found on the green capsules were green, whilst those on the brown capsules were of a corresponding colour.

On the whole I am inclined to believe that sufficient importance has not hitherto been given to phytophagic variability as a factor in determining larval coloration, and a large field for experimental investigation here lies open for future work. The obscure chemico-physiological processes which may perhaps be shown by such researches to lead to phytophagic variation, cannot, I am persuaded, produce any great divergence of character if unaided; but when such causes of variability play into the hands of natural selection variations of direct _protective advantage_ to the species, we can easily see that this all-important agency would seize upon and perpetuate such a power of adaptability to a variable environment. (See Proc. Zoo. Soc. 1873, p. 158, and “Nature,” vol. xiv., pp. 329 and 330.) R.M.]

[141] [In 1879 Mr. George Francis, of Adelaide, forwarded from the latter place a number of moths (a species of Anapæa) together with their larvæ (in alcohol) and cocoons (Proc. Ent. Soc. 1879, p. xvi), and in an accompanying note he stated that the male larva when living is of “a bright emerald green, with red and pink markings on the back, and yellow, black, and white streaks on the sides.” The male larva is described as being smaller than the female, and as possessing all the brilliant colours, the latter “having no red markings, but only white, yellow, and green, with a little black.” I was at first disposed to think that we might be dealing here with two distinct species having differently marked larvæ; but Mr. Francis this present year (1880) forwarded a large number of the living cocoons of this species, which I separated according to size, and, on the emergence of the moths (August), I found that all those from the small cocoons were males, and those from the larger cocoons females. There can be no doubt, therefore, that we have but one species in this case, the larva of which presents the remarkable phenomenon of sexual difference of coloration. As an analogous fact I may here mention the well-known case of _Orgyia Antiqua_, the larva of which differs in the colour of the tufts of hair according to sex. R.M.]

[142] [I have already given reasons for suspecting that the colour of green caterpillars may be due to the presence of chlorophyll (or some derivative thereof) in their tissues (see Proc. Zoo. Soc. 1873, p. 159). This substance appears to be one of great chemical stability, and, according to Chautard, who has detected it in an unaltered state in the tissues of certain leaf-feeding insects by means of its absorption spectrum (“Comp. Rend.” Jan. 13th, 1873), it resists the animal digestive processes (Ann. Ch. Phys. [5], iii., 1-56). If this view should be established by future observations, we must regard the green colour of caterpillars as having been produced, when protective, from phytophagic variability by the action of natural selection; and the absence of colour in internal feeders, above referred to, is only secondarily due to the exclusion of light, and depends primarily on the absence of chlorophyll in their food. In connection with this I may adduce the fact, that some few species of _Nepticula_ (_N. Oxyacanthella_, _N. Viscerella_, &c.) are green, although they live in leaf-galleries where this colour can hardly be of use as a protection; but their food (hawthorn and elm) contains chlorophyll. See also note 130, p. 293. Further investigations in this direction are much needed. R.M.]

[143] [The same applies to _Pseudoterpna Cytisaria_, also feeding on broom at the same time of the year. The most striking cases of adaptive resemblance brought about by longitudinal stripes are to be found among fir and pine feeders, species belonging to the most diverse families (_Hyloicus Pinastri_, _Trachea Piniperda_, _Fidonia Piniaria_, &c., &c.) all being most admirably concealed among the needle-shaped leaves. R.M.]

[144] The geographical distribution of the dark form indicates that in the case of this species also, the form referred to is replacing the yellow (green) variety. Whilst in the middle of Europe (Germany, France, Hungary) the dark form is extremely rare, in the south of Spain this variety, as I learn from Dr. Noll, is almost as common as the yellow one. I hear also from Dr. Staudinger that in South Africa (Port Natal) the dark form is somewhat the commoner, although the golden-yellow and, more rarely, the green varieties, occur there. I have seen a caterpillar and several moths from Port Natal, and these all agree exactly with ours. The displacement of the green (yellow) form by the dark soil-adapted variety, appears therefore to proceed more rapidly in a warm than in a temperate climate. [Eng. ed. Dr. Noll writes to me from Frankfort that the caterpillar of _Acherontia Atropos_ in the south of Spain does not, as with us, conceal itself by day in the earth, but on the stems underneath the leaves. “At Cadiz, on the hot, sandy shore, _Solanum violaceum_ grows to a height of three feet, and on a single plant I often found more than a dozen _Atropos_ larvæ resting with the head retracted. It can easily be understood why the lateral stripes are blue when one has seen the south European _Solaneæ_, on which this larva is at home. _Solanum violaceum_ is scarcely green: violet tints alternate with brown, green, and yellow over the whole plant, and between these appear the yellow-anthered flowers, and golden-yellow berries of the size of a greengage. Thus it happens that the numerous thorns, an inch long, between which the caterpillar rests on the stem, pass from violet into shades of blue, red, green, and yellow.”]

[145] [For Mr. J. P. Mansel Weale’s remarks on the habits of certain ocellated S. African Sphinx-larvæ see note 129, p. 290. R.M.]

[146] [Some experiments with the caterpillar of _C. Elpenor_, confirming these results, have been made by Lady Verney. See “Good Words,” Dec. 1877, p. 838. R.M.]

[147] [The eye-spots on _Ch. Nerii_ have thus been supposed by some observers to be imitations of the flowers of the periwinkle, one of its food-plants. See, for instance, Sir John Lubbock’s “Scientific Lectures,” p. 51. R.M.]

[148] “On Insects and Insectivorous Birds,” Trans. Ent. Soc. 1869, p. 21.

[149] _Ibid._, p. 27.

[150] [Messrs. Weir and Butler inform me that they have not experimented with Sphinx-larvæ. R.M.]

[151] [It appears that the nauseous character of these last butterflies is to a certain extent retained after death, as I found that in an old collection which had been destroyed by mites, the least mutilated specimens were species of _Danais_ and _Euplæa_, genera which are known to be distasteful when living, and to serve as models for mimicry. See Proc. Ent. Soc. 1877, p. xii. R.M.]

[152] [This bears out the view expressed in a previous note 129, p. 290, that the grotesque attitude and caudal tentacles are more for protection against ichneumons than against larger foes. R.M.]

[153] These experiments, as already mentioned above, were not made with the common German lizard (_Lacerta Stirpium_), but with the large South European _Lacerta Viridis_.

[154] Thus, Boisduval states of this caterpillar, which in Provence lives on _Euphorbia esula_ and allied species:--“Its resemblance to a serpent, and its brilliant colour, permit of its being easily discovered.” This was written in 1843, long before natural selection was thought of.

[155] Or some other extinct analogously-marked species.

[156] [See Darwin’s remarks on the struggle for life being most severe between individuals and varieties of the same species “Origin of Species,” 6th ed. p. 59. R.M.]

[157] [Compare this with Darwin’s remarks on “analogous variations,” “Origin of Species,” 6th ed., p. 125. R.M.]

[158] “Zoologische Studien auf Capri. II. Lacerta muralis cærula, ein Beitrag zur Darwin’schen Lehre.” Leipzig, 1874. [The subject of colour-variation in lizards has been much discussed in “Nature” since the publication of the above mentioned essay; see vol. xix., pp. 4, 53, 97, and 122, and vol. xx., pp. 290 and 480. R M.]

[159] “Über die Berechtigung der Darwin’schen Theorie.” Leipzig, 1868. See also the previous essay “On the Seasonal Dimorphism of Butterflies,” pp. 112-116.

[160] [Mr. A. G. Butler has recently advanced the view that this family is not allied to the _Sphingidæ_, but is related on the one side to the _Pyrales_, and on the other to the _Gelechiidæ_. See his paper “On the Natural Affinities of the Lepidopterous Family _Ægeriidæ_,” Trans. Ent. Soc. 1878, p. 121. R.M.]

[161] I am indebted to my esteemed colleague, Prof. Gestäcker, for the knowledge of this specimen.

[162] Cat. Lep. East India Co., Pl. VIII.

[163] Such a residue is distinctly visible in _S. Ocellatus_: see Fig. 70, Pl. VII.

[164] [The question here also suggests itself as to why the _dorsal_ line should not have been the primary longitudinal stripe, seeing that such a marking is almost naturally produced in many caterpillars by the food in the alimentary canal; or, in other words, why has not natural selection taken advantage of such an obvious means of producing a stripe in cases where it would have been advantageous? In answer to this I may state, that in large numbers of species the dorsal line has thus become utilized; but in the case of large caterpillars resting among foliage, it can be easily seen that light lateral (_i.e._ subdorsal) stripes, are more effective in breaking the homogeneity of the body than a dorsal line only slightly darker than the general ground-colour. Lateral lines are in fact visible from _two directions of space_. If a caterpillar thus marked be placed on a twig, these lines are visible when we look at the creature’s back or at either side. That the subdorsal are therefore the primary lines, as shown by Dr. Weismann’s observations of the ontogeny of many of the _Sphingidæ_, is quite in harmony with the view of their having been produced by natural selection. R.M.]

[165] “Die Darwin’sche Theorie. Elf Vorlesungen über die Entstehung der Thiere und Pflanzen durch Naturzüchtung.” 2nd ed., Leipzig, 1875, p. 195.

[166] [In the following species, already mentioned in previous notes, the oblique stripes are bounded at their upper extremities by a conspicuous subdorsal line:--_Acosmeryx Anceus_, Cram.; _Sphinx Cingulata_, Fabr.; _Pachylia Ficus_, Linn.; _P. Syces_, Hübn. In _Pseudosphinx Cyrtolophia_, Butl., the oblique white stripes, beautifully shaded with pink, run into the white pink-bordered dorsal line, so that when seen from above the markings present the appearance of the midrib and lateral veins of a leaf, and are probably specially adapted for this purpose. R.M.]

[167] [The dorsal line as well as the oblique stripes is present in the caterpillar of _Smerinthus Tartarinovii_, Ménét.; and in _Ambulyx Gannascus_, Stoll., the oblique stripes are bounded above by a subdorsal line, as in the species named in the preceding note. R.M.]

[168] Cat. Lep. East India Co., Pl. XI.

[169] [Compare this with Darwin’s “Origin of Species” (1st. ed. p. 440), where it is stated that when an animal, during any part of its embryonic career, is active, and has to provide for itself, “the period of activity may come on earlier or later in life; but whenever it comes on, the adaptation of the larva to its conditions of life is just as perfect and beautiful as in the adult animal. From such special adaptations the similarity of the larvæ or active embryos of allied animals is sometimes much obscured.” R.M.]

[170] [For Fritz Müller’s application of this principle to the case of certain groups of Brazilian butterflies see Appendix II. to this Part. R.M.]

Transcriber’s Notes

Punctuation, hyphenation, and spelling were made consistent when a predominant preference was found in this book; otherwise they were not changed.

Simple typographical errors were corrected; occasional unbalanced quotation marks were corrected.

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