Studies in the Theory of Descent, Volume I

On these grounds I designate the phenomenon as “polymorphism,” although it may not yet have reached, as such, its sharpest limits. This would be brought about by the elimination of the intermediate forms.[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 (#Page_32), note 20 (#cn_23)) 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.]]

Immediately before pupation, all the caterpillars, both green and brown, acquire a lilac coloration. The fifth stage lasts seven days, and the whole larval development twenty-three days, the period from the deposition of the eggs to the appearance of the moth being only thirty-one days.

I have treated of the polymorphism of Stellatarum in detail, not only because it has hitherto remained unknown, and an analysis of such cases has been completely ignored,[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.]] but more particularly because, it appears to me, that important conclusions can be drawn therefrom. Moreover, such an extreme multiplicity of forms is interesting, since, so far as I know, polymorphism to this extent has not been observed in any insect.

The theoretical bearing of this polymorphism will be treated of subsequently. It is not in any way connected with a more advanced development of the markings, since M. Stellatarum shows in this respect a very low state of development. This species displays only two stages: – (1), complete absence of all markings; and (2), a simple subdorsal, with dorsal and spiracular lines. We must therefore admit that the phyletic development of the markings has for a long time remained at a standstill, or, what expresses the same thing, that the marking which the adult larva now possesses is extremely old.

In order to complete my observations on M. Stellatarum, I now add some remarks on the pupa, the colour variations of which it appeared of importance to investigate, owing to the extraordinary variability of the caterpillar. The pupa varies but very slightly; the ochreous yellow ground-colour sometimes passes into reddish, and sometimes into greenish; the rather complicated blackish-brown marking of streaky lines is very constant, especially on the wing portions, being at most only more or less strongly pronounced. The minute colour variations of the pupa therefore have no connection with the colour of the caterpillar, both green and brown larvæ furnishing sometimes reddish-yellow and sometimes greenish-yellow pupæ.

The comparison of M. Stellatarum with the other known species of the genus, brings scarcely any addition to our knowledge of the phyletic development. Thus, the two European species of which the caterpillars are known, viz. M. Fuciformis and Bombyliformis,[110 - [In Butler’s revision both these species are placed in the genus Hemaris. R.M.]] show essentially the same markings as Stellatarum, the chief element being a well-developed subdorsal line. The Indian M. Gilia, Herrich-Schäf., possesses also this line,[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.]] and, together with the East Indian M. Corythus, Walk.,[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.]] has oblique stripes in addition; the stripes do not, however, cross this line, but commence underneath it, and probably originated at a later period than the subdorsal line. Should this be the case, we must regard M. Corythus as representing a later phyletic stage. According to Duponchel’s figures, in both M. Fuciformis and Bombyliformis small oblique stripes (red) occur near the spiracles, but these have nothing to do with the oblique stripes of M. Gilia just mentioned, as they run in a contrary direction. Of the two European species, I have only seen the living caterpillar of Fuciformis, and this possessed no oblique stripes.

To these five species I am now enabled to add a sixth, viz. Macroglossa Croatica,[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.]] a species inhabiting Asia Minor and Eastern Europe, of which a specimen and notice were kindly forwarded to me by Dr. Staudinger. The adult caterpillar much resembles that of M. Stellatarum in form and marking, but the subdorsal line appears much less distinctly defined, and the dorsal and spiracular lines seem to be entirely absent. The colour is generally green, but varies to red, and the subdorsal is more distinct and sharper in the young than in the adult larva. The markings of this species do not therefore in any way surpass those of Stellatarum, but are, on the contrary, much simpler.[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.]]

THE GENUS PTEROGON, BOISD.[115 - [Genus Pterogon, Boisd., = Proserpinus and Lophura (part). Butler, loc. cit. p. 632. The species above treated of = Proserpinus Œnotheræ, Fabr. R.M.]]

Although I am acquainted with only a small portion of the developmental history of a single species of this genus, I will here proceed to record this fragment, since, taken in connection with two other species, it appears to me sufficient to determine, at least broadly, the direction of development which this genus has taken.

Pterogon Œnotheræ, Fabr

The adult larva, as made known by many, and for the most part good figures, has very complicated markings, which do not seem derivable from any of the elements of marking in the Sphingidæ hitherto considered. I was therefore much surprised at finding a young caterpillar of this species, only twelve millimeters in length, of a light green colour, without any trace of the subsequent latticed marking, and with a broad white subdorsal line extending along all the twelve segments. (Pl. VII., Fig. 63). Judging from the size and subsequent development, this caterpillar was probably in the third stage.

The same colouring and marking remained during the following (fourth) stage; but in the position occupied by the caudal horn in other Sphingidæ, there could now be observed the rudiment of a future ocellus in the form of a round yellowish spot (Pl. VII., Fig. 64). The subdorsal line disappears suddenly in the fifth stage, when the larva becomes dark green (rarely) or blackish-brown; the latticed marking and the small oblique stripes are also acquired, together with the beautifully developed eye-spots, consisting of a yellow mirror with black nucleus and ground-area (Pl. VII., Fig. 65).

The North American Pterogon Gauræ and P. Abboti[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.]] also show markings precisely similar to those of this European species in the adult state; but in the two former the markings are of special interest as indicating the manner in which the primary Sphinx-marking has become transformed into that of the apparently totally different adult P. Œnotheræ. P. Gauræ is green, with a complicated latticed marking, which closer observation shows to arise from the dorsal line being resolved into small black dots, whilst the subdorsal line is broken up into black, white-bordered triangles. This caterpillar therefore gives fresh support to the remarkable phenomenon that the animals as well as the plants of North America are phyletically older than the European fauna and flora, a view which also appeared similarly confirmed by Deilephila Lineata, the representative form of D. Livornica. In entire accordance with this is the fact that the larva of P. Gauræ is without the eye-spot on the eleventh segment, and instead thereof still shows the original although small caudal horn. The perfect insect also resembles our P. Œnotheræ in colour and marking, but not in the form of the wings.

That the caterpillars of the genus Pterogon originally possessed the caudal horn we learn from P. Gorgoniades, Hübn.,[117 - [Proserpinus (Sphinx) Gorgon, Esp. R.M.]] a species now inhabiting south-east Russia, and for a knowledge of which I am indebted to Dr. Staudinger’s collection. There are in this about eight blown specimens, from 3.7 to 3.9 centimeters in length, which show a marking, sometimes on a red and sometimes on a green ground, which unites this species with the young form of P. Œnotheræ, viz., a broad white subdorsal line, extending from the small caudal horn to the head. In addition to this, however, the caterpillar possesses an extraordinarily broad white red-bordered infra-spiracular line, a fine white dorsal stripe, and a similar line between the subdorsal and spiracular, i. e. a supra-spiracular line.

The caterpillars in Staudinger’s collection, notwithstanding their small size, all belong to the last stage, as the moth itself does not measure more than 2.6 centimeters in expanse, and is therefore among the smallest of the known Sphingidæ. This species has therefore in the adult condition a marking very similar to that of Œnotheræ when young – it bears to Œnotheræ the same relationship that Deilephila Hippophaës does to D. Euphorbiæ, only in the present case the interval between the two species is greater. Gorgoniades is obviously a phyletically older species, as we perceive from the marking and from the possession of a horn. We certainly do not yet know whether Œnotheræ possesses a horn in its earliest stages, although in all probability it does so; in any case the ancestor of Œnotheræ had a horn, since the closely allied P. Gauræ now possesses one.

We thus see that also in the genus Pterogon the marking of the caterpillars commences with a longitudinal line formed from the subdorsal; an infra-spiracular or also a supra-spiracular line (Gorgoniades) being added. A latticed marking is developed from the linear marking by the breaking up of the latter into spots or small patches, which finally (in Œnotheræ) become completely independent, their connection with the linear marking being no longer directly perceptible.

THE GENUS SPHINX, LINN

Of this genus (in the narrow sense employed by Gray) I have only been able, in spite of all trouble, to obtain fertile eggs of one species. The females cannot be induced to lay in confinement, and eggs can only be obtained by chance.

I long searched in vain the literature of this subject for some account of the young stages of these caterpillars, and at length found, in a note to Rösel’s work, an observation of Kleemann’s on the young forms of Sphinx Ligustri, which, although far from complete, throws light on certain points.

From a female of S. Ligustri Kleemann obtained 400 fertile eggs. The caterpillars on emerging are “at first entirely light yellowish-green, but become greener after feeding on the fresh leaves;” the horn is also at first light green, and then becomes “darker.” The young larvæ spin webs, by which they fasten themselves to the leaves of their food-plant (this, so far as I know, has not been observed in any species of Sphingidæ). They moult four times, the border round the head and the purple stripes appearing after the third moult, these stripes “having previously been entirely white.” The ecdyses follow at intervals of about six days, increasing to about ten days after the fourth moult.[118 - Rösel, loc. cit. vol. iii., p. 26, note.]

From this short account we gather that in the third stage the marking consists of seven oblique white stripes, which acquire coloured edges in the fourth stage, a fact which I have myself frequently observed. On the most important point Kleemann’s observations unfortunately give no information – the presence or absence of a subdorsal line in the youngest stages. That he does not mention this character, can in no way be considered as a proof of its actual absence. I am rather inclined to believe that it is present in the first, and perhaps also in the second stage. There occur, however, species of the genus Sphinx (sensû strictiori) which possess a subdorsal line when young, as I think may be certainly inferred from the fact that the remains of such a line are present in the adult larva of S. Convolvuli.

This conclusion becomes still more certain on comparing the markings with those of a nearly allied genus; without such comparison the separation of the genus Macrosila, Boisd., from Sphinx is scarcely justifiable. If to these two genera we add Dolba, Walk., and Acherontia, Ochs., we must be principally struck with the great similarity in the markings, which often reaches to such an extent that the differences between two species consist entirely in small shades of colour, while the divergence of the moths is far greater.

Of the genera mentioned, I am acquainted altogether with fourteen species of caterpillars: —Macrosila Hasdrubal, Rustica,[119 - Figured and described by Abbot and Smith. [Macrosila (Sphinx) Cingulata is figured also by Burmeister, loc. cit. Pl. XII., Fig. 1. R.M.]] and Cingulata;119 (#cn_122)Sphinx Convolvuli, Ligustri, Carolina,119 (#cn_122)Quinquemaculata,119 (#cn_122)Drupiferarum,119 (#cn_122)Kalmiæ,119 (#cn_122) and Gordius;119 (#cn_122)Dolba Hylæus;119 (#cn_122)Acherontia Atropos, Styx,[120 - Figured in “Cat. Lep. E. Ind. Co.”] and Satanas.120 (#cn_123) With one exception all these caterpillars possess oblique stripes of the nature of those of the Smerinthus larvæ, and most of them are without any trace of a subdorsal line; one species – the North American M. Cingulata– has a completely developed subdorsal; and the typical European species, S. Convolvuli, has a rudimentary subdorsal line. The ground-colour in most of these species is of the same green as that of the leaves of their food-plants; some are brown, i. e. earth-coloured, and in these the markings do not appear so prominently; others again possess very striking colours (A. Atropos), the oblique stripes in these cases being very vivid. Only M. Hasdrubal[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.]] separates itself completely from this system of classification, since this species is deep black with narrow yellow rings, the horn and last segment being red.

The large and most striking caterpillar of M. Hasdrubal is the same which Wallace has made use of for his theory of the brilliant colours of caterpillars. The explanation of the origin of this widely divergent mode of marking could only be furnished by the ontogeny, in which one or another of the older phyletic stages will certainly have been preserved.

Strictly speaking the same should be said of the other species – nevertheless their comparison with the so similarly marked Smerinthinæ, together with the circumstance that in certain species a subdorsal line can be traced, makes it appear correct to suppose that here also the subdorsal was the primary marking, this line being subsequently entirely replaced by the oblique stripes. The Sphinginæ would therefore be a younger group than the Smerinthinæ, a conclusion which is borne out by the fact that in the former the oblique stripes have reached a higher development, being always of two, and sometimes even of three colours (S. Drupiferarum, white, red, black), whilst in the species of Smerinthus they only occasionally possess uniformly coloured borders.

THE GENUS ANCERYX, BOISD

Although this genus is not admitted into most of the European catalogues – the solitary European species representing it being referred to the genus Sphinx, Linn.[122 - [The species referred to is placed by Butler in Hübner’s genus Hyloicus. R.M.]]– its separation from Sphinx appears to me to be justified, not because of the striking differences presented by the moths, but because the caterpillars, judging from the little we know of them, likewise show a similar degree of difference.

I have frequently succeeded in obtaining fertile eggs of Anceryx Pinastri and I will now give the developmental history of this caterpillar, which has already been figured with great accuracy in Ratzeburg’s excellent work on forest insects. Rösel was acquainted with the fact that the “pine moth” laid its eggs singly on the needles of the pine in June and July, and he described them as “yellowish, shining, oval, and of the size of a millet seed.”

On emerging, the caterpillars are six millimeters in length, of a light yellow colour, the head shining black with a yellow clypeus. The caudal horn, which is forked at the tip, is also at first yellowish, but soon becomes black. No particular marking is as yet present, but a reddish stripe extends along the region of the dorsal vessel, and the course of the spiracles is also marked by an orange-red line. (Fig. 53, A & B, Pl. VI.)

As soon as the young larvæ are filled with food they acquire a greenish streak. The first moult occurs after four days, and immediately after this there is still an absence of distinct markings, with the exception of a greenish-white spiracular line. In the course of some hours, however, the original light green ground-colour becomes darker, and at the same time a sharp, greenish-white subdorsal line appears, together with a parallel line extending above the spiracles, which, in Pterogon Gorgoniades, has already been designated as the “supra-spiracular.” The dorsal line is absent: the head is light green, with two narrow blackish-brown lines surrounding the clypeus; the horn and thoracic legs are black; claspers, reddish green; length, twelve to thirteen millimeters. (Fig. 54.)

Third Stage

After another period of four days the second moult occurs, neither colour nor marking being thereby affected. Only the horn, now no longer forked, becomes brownish with a black tip. The young caterpillars are now, as before, admirably adapted to the pine needles, on which they feed by day, and from which they can only be distinguished with difficulty.

Fourth Stage

The third moult also brings no essential change. The ground-colour and marking remain the same, only the spiracles, which were formerly dull yellowish, are now of a vivid brick-red. The horn becomes yellowish-red at the base.

Fifth Stage

The marking is only completely changed in the fifth and last stage. A broad reddish-brown dorsal line replaces the subdorsal, more or less completely. The supra-spiracular line also becomes broken up into numerous short lengths, whilst the green ground-colour in some specimens becomes more or less replaced by a brownish shade extending from the back to the sides. Horn, black; the upper part of the first segment with a corneous plate, similar to that of the Deilephila larvæ.

This stage is very variable, as shown by the figures in various works. The variations arise on the one hand from the struggle between the green ground-colour and the reddish-brown extending from above, and, on the other hand, from a more or less complete disappearance of the associated longitudinal lines. The latter are sometimes completely retained, this being the case in a caterpillar figured by Hübner (Sphinges, III., Legitimæ C, b), where both the subdorsal and supra-spiracular lines are continuous from segment 11 to segment 1, an instance which may perhaps be regarded as a reversion to the primary form.

The entire change of the marking from the fourth to the fifth stage depends upon the fact that the young larvæ resemble the needles of the pine, whilst the adults are adapted to the branches. I shall return to this later.

The ontogeny of A. Pinastri makes us acquainted with three different forms of marking: (1) simple coloration without marking; (2) a marking composed of three pairs of parallel longitudinal lines; (3) a complicated marking, arising from the breaking up of the last and the addition of a darker dorsal line.

Of the fourteen species placed by Gray in the genus Anceryx, I find, in addition to the one described, notices of only two caterpillars: —

A. Coniferarum,[123 - [= Ellema Coniferarum, of Butler’s revision. R.M.]] a North American species, lives on Pinus Palustris, and was figured by Abbot and Smith. Colour and marking very similar to A. Pinastri.

A. Ello, Linn.,[124 - [= Dilophonota Ello of Butler’s revision. R.M.]] according to the authority of Mérian, is described by Clemens[125 - “Synopsis of the North American Sphingides.” Philadelphia, 1859.] as dark brown, “with a white dorsal line, and irregular white spots on the sides.” It lives on a “species of Psidium or Guava.”

Most of the species of Anceryx appear to live on Coniferæ, to which they show a general and decided adaptation. In the absence of decisive information, I partly infer this from the names, as Anceryx Juniperi (Africa). It has long been known that in our A. Pinastri the mixture of brown and fir-green, interspersed with conspicuous irregular light yellowish and white spots, causes the adult larva to present a very perfect adaptation to its environment. Of this caterpillar Rösel states: – “After eating it remains motionless, and is then difficult to see, because it is of the same colour as its food, since its brown dorsal line has almost the colour of the pine twigs; and who is not familiar with the fact that beneath the green needles there is also much yellow to be found?”

This adaptation to the needles and twigs obviously explains why this caterpillar in the adult condition is so far removed from those of the genus Sphinx, while the moths are so nearly related that they were only separated as a distinct genus when we became acquainted with a large number of species.

II. Conclusions from Phylogeny

The considerations previously set forth are entirely based on Fritz Müller’s and Haeckel’s view, that the development of the individual presents the ancestral history in nuce, the ontogeny being a condensed recapitulation of the phylogeny.

Although this law is generally true – all recent investigations on development having given it fresh confirmation – it must not be forgotten that this “recapitulation” is not only considerably abbreviated, but may also be “falsified,” so that a searching examination into each particular case is very desirable.

The question thus arises, in the first place, as to whether the markings of caterpillars, so distinct at the different stages of growth, are actually to be regarded as residual markings inherited from the parent-form; or whether their differences do not depend upon the fact that the caterpillar, in the course of growth, is exposed to different external conditions of life, to which it has adapted itself by assuming a different guise.

The former is undoubtedly the case. It can by no means be denied that the conditions of life in young caterpillars are sometimes different to those of the adults. It will, in fact, be shown later on, that in certain cases the assumption of a new guise at an advanced age actually depends upon adaptation to new conditions of life; but as a rule, the external conditions remain very similar during the development of the larva, as follows from the fact that a change of food-plant never takes place.[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.]] We should therefore rather expect a complete similarity of marking throughout the entire larval period, instead of the great differences which we actually observe.

Different circumstances appear to me to show that the markings of young larvæ are only exceptionally due to a new adaptation, but that as a rule they depend upon heredity. In the first place, there is the fact that closely allied species, exposed to precisely similar external conditions, as, for instance, Chærocampa Elpenor and Porcellus, possess exactly the same markings when young, these markings nevertheless appearing at different stages of growth. Thus, the subdorsal line first appears in Elpenor in the second stage, whilst in Porcellus it is present during the first stage. If this line were acquired by the young larva for adapting it at this age to special conditions of life, it should appear in both species at the same stage. Since this is not the case, we may conclude that it is only an inherited character derived from the adult ancestor of the two species, and now relegated to the young stages, being (so to speak), pushed further back in one species than in the other.