Studies in the Theory of Descent, Volume I

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.]