Chapter XXIV: Introduction (4)

[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.]

[171] [The slight variability in the colour of this pupa, opens up the interesting question of the photographic sensitiveness of this and other species, which is stated to cause them to assimilate in colour to the surface on which the larva undergoes its final ecdysis. Some experiments upon this subject have been recorded by Mr. T. W. Wood, Proc. Ent. Soc. 1867, p. xcix, but the field is still almost unexplored. R.M.]

[172] “Über den Einfluss der Isolirung auf die Artbildung.” Leipzig, 1872, p. 20.

[173] In some instances _Deilephila Lineata_ has also been seen by day hovering over flowers.

[174] It is true that I only reared one brood, but from this fifty specimens were obtained. It would be interesting to know whether this variety of the caterpillar is distributed over the whole of Southern Europe.

[175] In this sense Lubbock says:--“It is evident that creatures which, like the majority of insects, live during the successive periods of their existence in very different circumstances, may undergo considerable changes in their larval organization in consequence of forces acting on them while in that condition; not, indeed, without affecting, _but certainly without affecting to any corresponding extent_, their ultimate form.”--“Origin and Metamorphoses of Insects,” London, 1874, p. 39.

[176] “Grundzüge der Zoologie,” 1875.

[177] [Lepidopterists are of course aware that even these distinctions are not absolute, as no single character can be named which does not also appear in certain moths. The definition in this case, as in that of most other groups of animals and plants, is only a general one. See, for instance, Westwood’s “Introduction to the Classification of Insects,” vol. ii. pp. 330-332. Also some remarks by C. V. Riley in his “Eighth Annual Report” on the insects of Missouri, 1876, p. 170. With reference to the antennæ as a distinguishing character, see Mr. A. G. Butler’s article in “Science for All,” 1880, part xxvii. p. 65. R.M.]

[178] The genus of _Morphinæ, Discophora_, possesses hairs very similar to those of the genus _Cnethocampa_ belonging to the _Bombycidæ_.

[179] [The larvæ of genera 14, _Phyciodes_, and 35, _Crenis_, are likewise spiny. See Edwards’ “Butt. of N. Amer.” vol. ii. for figures of the caterpillar of _Phyc. Tharos_: for notes on the larvæ of _Crenis Natalensis_ and _C. Boisduvali_ see a paper by W. D. Gooch, “Entomologist,” vol. xiv. p. 36. The larvæ of genus 55, _Ageronia_, are also spiny. (See Burmeister’s figure of _A. Arethusa_, “Lép. Rép. Arg.” Pl. V. Fig. 4). The larvæ of genus 98, _Aganisthos_, also appear to be somewhat spiny (see Burmeister’s figure of _A. Orion_, _loc. cit._ Pl. V. Fig. 6), and this raises the question as to whether the genus is correctly located in its present position. The larvæ of the following genera figured in Moore’s “Lepidoptera of Ceylon,” parts i. and ii., are all spiny:--6, _Cirrochroa_ (Pl. XXXII.); 7, _Cynthia_ (Pl. XXVI.); 27, _Kallima_ (Pl. XIX.); and 74, _Parthenos_ (Pl. XXIV.). Many species of caterpillars which are spiny when adult appear to be spineless, or only slightly hairy when young. See Edwards’ figures of _Melitæa Phaeton_, _Argynnis Diana_, and _Phyc. Tharos_ (_loc. cit._) and his description of the larva of _Arg. Cybele_, “Canad. Entom.” vol. xii. p. 141. The spiny covering thus appears to be a character acquired at a comparatively recent period in the phyletic development. R.M.]

[180] [The larvæ of the 110th genus, _Paphia_, Fabr. (_Anæa_, Hübn.) are also smoothed-skinned. See Edwards’ figure (_loc. cit._ vol. i. Pl. XLVI.) of _P. Glycerium_. Also C. V. Riley’s “Second Annual Report” on the insects of Missouri, 1870, p. 125. Burmeister figures the larva of a species of _Prepona_ (genus 99) which is smooth (_P. Demophon_, _loc. cit._ Pl. V. Fig. 1). The horns on the head of _Apatura_, &c., may possibly be a survival from a former spiny condition. R.M.]

[181] “Synopsis of the described Lepidoptera of North America.” Washington, 1862.

[182] “Catalog der Lepidopteren des Europäischen Faunengebietes.” Dresden, 1871.

[183] This group of moths (“Schwärmer”) is regarded as of very different extents by systematists; when I here comprise under it only the _Sphingidæ_ proper and the _Sesiidæ_, I by no means ignore the grounds which favour a greater extension of the group; the latter is not rigidly limited. [The affinities of the _Sesiidæ_ (_Ægeriidæ_) are by no means clearly made out: it appears probable that they are not related to the _Sphingidæ_. See note 160, p. 370. R.M.]

[184] [For Mr. A. G. Butler’s observations on the genus _Acronycta_, see “Trans. Ent. Soc.” 1879, p. 313; and note 68, p. 169, of the present volume. R.M.]

[185] [The following characters are given in Stainton’s “Manual of British Butterflies and Moths,” vol. i. p. 114:--“Larva of very variable form: at one extreme we find the singular _Cerura_ larvæ, with only fourteen legs, and two long projecting tails from the last segment; at the other extreme we have larvæ with sixteen legs and no peculiarity of form, such as _Chaonia_ and _Bucephala_; most have, however, the peculiarity of holding the hind segment of the body erect when in repose; generally quite naked, though downy in _Bucephala_ and rather hairy in _Curtulu_; very frequently there are projections on the back of the twelfth segment.” R.M.]

[186] Encyl. Meth. ix. p. 310.

[187] [The genus _Vanessa_ (in the wide sense) appears to be in a remarkable condition of what may be called phyletic preservation. Thus, the group of species allied to _V. C.-album_ passes by almost insensible steps into the group of butterflies typified by our “Tortoiseshells.” The following is a list of some of the intermediate species in their transitional order:--_I.-album_, _V.-album_, _Faunus_, _Comma_, _California_, _Dryas_, _Polychloros_, _Xanthomelas_, _Cashmirensis_, _Urticæ_, _Milberti_, &c. Similarly, our _Atalanta_ and _Cardui_ are connected by a number of intermediate forms, showing a complete transition from the one to the other. The following is the order of the species so far as I am acquainted with them:--_Atalanta_, _Dejeanii_, _Callirhoë_, _Tammeamea_, _Myrinna_, _Huntera_, _Terpsichore_, _Carye_, _Kershawii_, and _Cardui_. R.M.]

[188] “Prodromus Systematis Lepidopterorum.” Regensburg, 1864.

[189] [The larva of _Acherontia Morta_, figured by Butler (see note 121, p. 262), possesses the characteristically recurved horn; that of _Ach. Medusa_ figured by the same author, does not appear to possess this character in any marked degree. R.M.]

[190] [See note 97, p. 233. R.M.]

[191] _Loc. cit._ Pl. XXV. [This species is referred by Butler to the genus _Paonias_, Hübn. R.M.]

[192] Abbot and Smith, Pl. XXIX. [Placed by Butler in the genus _Cressonia_, Grote and Robinson. Abbot and Smith state that this larva is sometimes green. According to Mr. Herman Strecker (Lepidop. Rhopal. and Hetero, Reading, Pa. 1874, p. 54) it feeds upon black walnut (_Juglans Nigra_), hickory (_Carya Alba_), and ironwood (_Ostrya Virginica_). Of the North American species of _Smerinthus_, the following, in addition to _Excæcatus_, closely resemble our _Ocellatus_:--_S. (Calasymbolus) Geminatus_, Say; _(C.) Cerisii_, Kirby; and _Ophthalmicus_, Boisd. In addition to _S. (Cressonia) Juglandis_, _S. (Triptogon) Modesta_ much resembles our _Populi_. The larva of _Geminatus_, according to Strecker, is “pale green, lightest above, with yellow lateral granulated stripes; caudal horn violet; stigmata red. It feeds on the willow.” R.M.]

[193] Cat. Brit. Mus.

[194] [This lengthening of the true legs is mimetic according to Hermann Müller, and causes the anterior portion of the caterpillar to resemble a spider. See note 129, p. 290. R.M.]

[195] [Certain butterflies appear to be crepuscular, if not nocturnal in their habits. Thus in his “Notes on the Lepidoptera of Natal,” Mr. W. D. Gooch states that he never saw _Melanitis_, _Leda_, or _Gnophodes Parmeno_ on the wing by day, but generally during the hour after sunset. He adds:--“My sugar always attracted them freely, even up to 10 or 11 p.m.” Many species of _Hesperidæ_ are also stated to be of crepuscular habits by this same observer. See “Entomologist,” vol xvi. pp. 38 and 40. R.M.]

[196] I only make this assumption for the sake of simplicity, and not because I am convinced that the existing _Rhopalocera_ are actually the oldest Lepidopterous group.

[197] Zeitschrift für wissenschaftl. Zoologie, vol. xx. p. 519.

[198] [See for instance Lubbock’s “Origin and Metamorphoses of Insects,” chap. iii.; and F. M. Balfour’s “Comparative Embryology,” vol. i., 1880, pp. 327--356. This last work contains an admirable _résumé_ of our knowledge of the embryonic development of insects up to the date of publication. R.M.]

[199] Are not the 4th, 11th, and 12th segments destitute of the rudiments of legs as in the larvæ of all existing saw-flies? I might almost infer this from Bütschli’s figures (see for instance Pl. XXV., Fig. 17A).

[200] [The grub-formed Hymenopterous larvæ, like the larvæ of all other holometabolous insects, thus represent an acquired degenerative stage in the development, _i.e._ an adaptation to the conditions of life at that stage. Bearing in mind the above-quoted observations of Bütschli and the caterpillar-like form of the Terebrantiate group of Hymenopterous larvæ, the following remarks of Balfour’s (_loc. cit._ p. 353), appear highly suggestive:--“While in a general way it is clear that the larval forms of insects cannot be expected to throw much light on the nature of insect ancestors, it does nevertheless appear to me probable that such forms as the caterpillars of the Lepidoptera are not without a meaning in this respect. It is easy to conceive that even a secondary larval form may have been produced by the prolongation of one of the embryonic stages; and the general similarity of a caterpillar to _Peripatus_, and the retention by it of post-thoracic appendages, are facts which appear to favour this view of the origin of the caterpillar form.” See also Sir John Lubbock, _loc. cit._, pp. 93 and 95. R.M.]

[201] [In the most recent works dealing with this order six groups, based on the character of the imagines are recognized, viz.:--_Tubulifera_, _Terebrantia_, _Pupivora_, _Heterogyna Fossores_, and _Mellifera_. (See, for instance, F. P. Pascoe’s “Zoological Classification,” 2nd ed. p. 147.) Of these groups the larvæ of the _Terebrantia_ as thus restricted are all of the caterpillar type (_Tenthredinidæ_ and _Siricidæ_), whilst those of the other groups are maggot-shaped. For a description of the development of the remarkable aberrant larva of _Platygaster_, see Ganin in Zeit. f. wissenschaftl. Zool., vol. xix. 1869. R.M.]

[202] [For recent investigations on the structure of the thorax in Diptera, see a paper by Mr. A. Hammond, in Journ. Linn. Soc., Zoology, vol xv. p. 9. R.M.]

[203] I am familiar with the fact that the two sub-orders of true Diptera, the short-horned (_Brachycera_), and the long-horned (_Nemocera_), are not sharply limited; and I am likewise well acquainted with the circumstance that there are forms which connect the two larval types. The connecting forms of the imagines do not, however, always coincide with the intermediate larval forms, so that there here arises a second and very striking incongruence of morphological relationship which depends only upon the circumstance that the one stage has diverged in form more widely than the other through a greater divergence in the conditions of life. The difficulty is in these cases aggravated because an apparent is added to the true form-relationship through convergence, so that without going into exact details the form and genealogical relationships of the Diptera cannot be distinguished. It would be of great interest for other reasons to make this investigation, and I hope to be able to find leisure for this purpose at some future period.

[204] “Entwicklung der Dipteren.” Leipzig, 1864.

[205] Lubbock concludes from the presence of thoracic legs in the embryonic larva of bees that these have been derived from a larva of the _Campodea_ type, but he overlooks the fact that the rudiments of the abdominal legs are also present; _loc. cit._, p. 28.

[206] “Für Darwin,” Leipzig, 1864, p. 8.

[207] Mem. Peabody Acad. of Science, vol. i. No. 3.

[208] Verhandl. Wien. Zoolog. Botan. Gesellsch. 1869, p. 310.

[209] Über Ontogenie und Phylogenie der Insekten. Eine akademische Preisschrift. Jen. Zeitschrift. Bd. x. Neue Folge, iii. Heft 2. 1876. [Some remarks by F. M. Balfour on the origin of certain larval forms have already been quoted in a previous note (p. 485). This author further states:--“The fact that in a majority of instances it is possible to trace an intimate connection between the surroundings of a larva and its organization proves in the clearest way _that the characters of the majority of existing larval forms of insects have owed their origin to secondary adaptations_. A few instances will illustrate this point:--In the simplest types of metamorphosis, _e.g._ those of the Orthoptera genuina, the larva has precisely the same habits as the adult. We find that a caterpillar form is assumed by phytophagous larvæ amongst the Lepidoptera, Hymenoptera, and Coleoptera. Where the larva has not to go in search of its nutriment the grub-like apodous form is assumed. The existence of such an apodous larva is especially striking in the Hymenoptera, in that rudiments of thoracic and abdominal appendages are present in the embryo and disappear again in the larva.... It follows from the above that the development of such forms as the Orthoptera genuina is more primitive than that of the holometabolous forms, &c.” Comparative Embryology, vol. 1, p. 352. R.M.]

[210] [The _Aphaniptera_ are now recognized in this country as a sub-order of Diptera. See, for instance, Huxley’s “Anatomy of Invertebrated Animals,” p. 425, and Pascoe’s “Zoological Classification,” 2nd ed. p. 122. R.M.]

[211] [This illustration of course only applies to the old arrangement of the Hymenoptera into _Terebrantia_ and _Aculeata_. See also note 201, p. 488. R.M.]

[212] [Eng. ed. This law is perhaps a little too restricted, inasmuch as it is theoretically conceivable that the organism may be able to adapt itself to similar conditions of life in different ways; differences of form could thus depend sometimes upon differences of adaptation and not upon differences in the conditions of life, or, as I have formerly expressed it, it is not necessary to allow always only _one_ best mode of adaptation.]

[213] [It must be understood that the word rendered here and elsewhere throughout this work as “transformation” is not to be taken in the narrow sense of metamorphosis, but as having the much broader meaning of a change of any kind incurred by an organism. Metamorphosis is in fact but one phase of transformation. R.M.]

[214] By the Editor.

[215] Mr. C. V. Riley in his excellent “Annual Reports” already quoted in previous notes, states that the larvæ of _Agrotis Inermis_, _Leucania Unipuncta_ (Army-worm), and _L. Albilinea_ are all loopers when newly hatched. (See First Report, p. 73; Eighth Report, p. 184; and Ninth Report, p. 53.)

[216] The following species not referred to in the previous part of this work are figured by Semper (Beit. zur Entwicklungsgeschichte einiger ostasiat. Schmet.; Verhandl. d. k.k. zoo. bot. Gesell. in Wien, 1867):--_Panacra Scapularis_, Walk.; _Chærocampa Clotho_, Drury; and _Diludia (Macrosila) Discistriga_, Walk. The following are figured by Boisduval and Guenée. (Spéc. Gén. 1874):--_Smerinthus Ophthalmicus_, Boisd.; _Sphinx Jasminearum_, Boisd.; _S. (Hyloicus) Plebeia_, Fabr.; _S. (Hyloicus) Cupressi_, Boisd.; _S. (Pseudosphinx) Catalpæ_, Boisd.; _Philampelus Jussiuæ_, Hübn. (= _Sphinx Vitis_, Linn.?); and _Ceratomia Amyntor_, Hübn. As the works of Abbot and Smith, and Horsfield and Moore have been exhausted by Dr. Weismann, it is quite unnecessary to extend this note by giving a list of the species figured by these authors.

[217] The same inference has already been drawn with respect to _Pterogon (Proserpinus) Œnotheræ_, see pp. 257, 258.

[218] This would of course be the _fourth_ segment if the head be considered the first, as on the Continent.

[219] “Second Annual Report,” 1870, p. 78.

[220] “Entomologist,” vol. xiv. p. 7.

[221] With reference to the habits of _C. Capensis_ (p. 531), I have since been informed by Mr. Trimen that this species does not conceal itself by day, so that the dimorphism may be regarded as a character retained from an earlier period and adapted to the present life conditions.

[222] “Kosmos,” Dec. 1877, p. 218. The paper is here introduced chiefly with a view to illustrate an important case of incongruence among Lepidopterous pupæ.

[223] [Maracujá, the local name for the Passiflora. R.M.]

[224] See p. 448.

[225] Verhandl. Schweiz. Naturforsch. Gesellschaft. Einsiedeln, 1868.

[226] [Eng. ed. In 1878 Señor José M. Velasco published a paper entitled “Description, metamorfosis. y costumbres de una especie nueva del genero _Siredon_.” Memor. Sociedad Mexicana de Historia Natural, December 26th. See Addendum to this essay.]

[227] Dana and Silliman’s Amer. Journ., 3rd series, i. p. 89. Annals Nat. Hist. vii. p. 246.

[228] Proc. Zoo. Soc. 1870, p. 160.

[229] Compt. Rend., vol. lx. p. 765 (1865).

[230] Nouvelles Archives du Muséum d’Histoire Nat. Paris, 1866, vol. ii. p. 268.

[231] Proc. Boston Soc., vol. xii. p. 97; Silliman’s Amer. Journ., vol. xlvi. p. 364; reference given in “Troschel’s Jahresbericht” for 1868, p. 37.

[232] Proc. Boston Soc., vol. xii. p. 97; Silliman’s Amer. Journ., vol. xlvi. p. 364. I have not been able to get a copy of this paper, and quote from a reference in “Troschel’s Jahresbericht.” See preceding note.

[233] Dana and Silliman’s Amer. Journ. See note 3.

[234] Proc. Acad. Philadelph. xix. 1867, pp. 166-209.

[235] Mém. Acad. Petersb. vol. xvi.

[236] [Eng. ed. Seidlitz is an exception, since in his work on Parthenogenesis (Leipzig, 1872, p. 13) he states that “In the Axolotl, Pædogenesis, which is not in this case ... monogamous, but sexual, and indeed gynækogenetic, has already become so far constant that it has perhaps entirely superseded the orthogenetic reproduction.”]

[237] Über den Einfluss der Isolirung auf die Artbildung. Leipzig, 1872, p. 33.

[238] Duméril represents the teeth of the _vomer_ as separated from those of the _os palatinum_ by a gap. This is probably accidental, since Gegenbaur (Friedrich u. Gegenbaur, the skull of Axolotl, Würzburg, 1849) figures the rows of teeth as passing over from the one bone to the other without interruption. This was the case with the Axolotls which I have been able to examine on this point; but this small discrepancy is, however, quite immaterial to the question here under consideration.

[239] See O. Hertwig “Über das Zahnsystem der Amphibien und seine Bedeutung für die Genese des Skelets der Mundhöhle.” Archiv. für microsc. Anat., vol. xi. Supplement, 1874.

[240] [Eng. ed. These Amblystomas have since died and have been minutely described by Dr. Wiedersheim. See his memoir, “Zur Anatomie des _Amblystoma Weismanni_,” in Zeit. für wiss. Zool., vol. xxxii. p. 216.]

[241] See Strauch, _loc. cit._ p. 10.

[242] See Part I. of this volume.

[243] [This is the principle of “Degeneration” recognized by Darwin (see “Origin of Species,” 6th ed. p. 389, and “Descent of Man,” vol. i. p. 206), and given fuller expression to by Dr. Anton Dohrn (see his work entitled “Der Ursprung der Wirbelthiere und das Princip des Functionswechsels.” Leipzig, 1875). A large number of cases have been brought together by Prof. E. R. Lankester, in his recent interesting work on “Degeneration, a Chapter in Darwinism.” Nature series, 1880. R.M.]

[244] “Sulla Larva del _Triton Alpestris_.” Archivio per la Zoologia. Genova e Torino, 1861, vol. i. pp. 206-211.

[245] See also Lubbock “On the Origin and Metamorphoses of Insects,” London, 1874.

[246] See the first essay “On the Seasonal Dimorphism of Butterflies,” p. 82.

[247] [Eng. ed. It has frequently been objected to me that the existing Axolotl is not a form resulting from atavism, but a case of “arrested growth.” The expression “atavism” is certainly to be here taken in a somewhat different sense than, for example, in the case of the reversion of the existing Axolotl to the Amblystoma form. Further on, I have myself insisted that in the first case the phyletic stage in which the reversion occurred is still completely preserved in the ontogeny of each individual, whilst the Amblystoma stage has become lost in the ontogeny of the Axolotl. If, therefore, we apply the term “atavism” only to such characters or stages (_i.e._ complexes of characters) as are no longer preserved in the ontogeny, we cannot thus designate the present arrest of the Axolotl at the perennibranchiate stage. Such a restriction of the word, however, appears to me but little desirable, since the process is identical in both cases, _i.e._ it depends upon the same law of heredity, in accordance with which a condition formerly occurring as a phyletic stage suddenly reappears through purely internal processes. It is true that the reversion is not _complete_, _i.e._ the present sexually mature Axolotl does not correspond in all details with its perennibranchiate ancestors. Since Wiedersheim has shown that the existing Axolotl possesses an intermaxillary gland, this can be safely asserted. This gland occurs only in _land_ Amphibians, and therefore originated with the Amblystoma form, afterwards becoming transferred secondarily to the larval stage. Nevertheless, the present Axolotl must resemble its perennibranchiate ancestors in most other characters, and we should be the more entitled to speak of a reversion to the perennibranchiate stage as we speak also of the reversion of single characters. To this must be added that the Axolotl does not correspond exactly with an Amblystoma larva, since Wiedersheim has shown that the space for the intermaxillary gland is present, but that the gland itself is confined to a few tubes which do not by any means fill up this space. (“Das Kopfskelet der Urodelen.” Morph. Jahrbuch, vol. iii. p. 149). By the expression “arrested growth” not much is said, if at the same time the cause of the arrest is left unstated. But what can be the cause why the whole organization remains stationary at the perennibranchiate stage, the sexual organs only undergoing further development? Surely only that law or force of heredity known by its effects, but obscure with respect to its causes, through which old phyletic stages sometimes suddenly reappear, or in other words, that power through which reversion takes place. It must not be forgotten that all these cases of “larval reproduction” in Amphibians appear suddenly. The present sexually mature form of the Axolotl has not arisen by the sexual maturity gradually receding in the ontogeny from generation to generation, but by the occurrence of single individuals which were sexually mature in the perennibranchiate stage, these having the advantage over the _Amblystomæ_ in the struggle for existence under changed climatic conditions.

By admitting a reversion, we perfectly well explain why arrest at the perennibranchiate stage can be associated with complete development of the sexual organs; the assumption of an “arrested growth” leaves this combination of characters completely unexplained. Moreover, I am of opinion that the expressions “arrested growth” or “reversion” are of but little importance so long as the matter itself is clear.]

[248] See Haeckel’s “Anthropogenie,” p. 449.

[249] “Der Ursprung der Wirbelthiere und das Princip des Functionswechsels,” Leipzig, 1875.

[250] Bull. Soc. Neuchâtel. vol. viii. p. 192. Reference given in “Troschel’s Jahresbericht” for 1869.

[251] Sitzungsberichte d. math. phys. Klasse der Akad. d. Wiss. zu München, 1875. Heft i.

[252] Compt. Rend. vol. lxviii. pp. 938 and 939.

[253] Archiv f. Naturgeschichte, 1867.

[254] Compt. Rend. vol. v. 1870, p. 70.

[255] Bull. Soc. Neuchâtel. vol. viii. p. 192. Reference given in “Troschel’s Jahresbericht” for 1869.

[256] [Eng. ed. It was mentioned in the German edition of this work that in the spring of 1876 a female Amblystoma of the Jardin des Plantes in Paris had laid eggs (see Blanchard in the Compt. Rend. 1876, No. 13, p. 716). Whether these eggs were fertile, or whether they developed was not then made known. Thus much was however at the time clear, that even if this had been the case, the reproduction of this Amblystoma would have been only an _exceptional_ occurrence. At that time there were in the Jardin des Plantes Amblystomas which had been kept for more than ten years, and only on one occasion was there a deposition of eggs, and this by only one specimen. That I was correct in speaking of the “sterility” of these Amblystomas in spite of this one exception, is proved by the latest communication from the Jardin des Plantes. We learn from this (Compt. Rend. No. 14, July, 1879, p. 108) that in the years 1877 and 1878 none of the Amblystomas laid any more eggs, although all means were exerted to bring about propagation. In April, 1879, eggs were again laid by one female, and by a second in May. These eggs certainly developed, as did those of 1876, and produced tadpoles. These Amblystomas are therefore not absolutely, but indeed relatively sterile. Whilst the Axolotl propagates regularly and freely every year, this occurs with the Amblystoma but rarely and sparsely. The degree of their sterility can only be approximately established when we know the number of Amblystomas that have since been kept in the Jardin des Plantes. Unfortunately nothing has been said with respect to this.]

[257] Origin of Species, 6th ed. p. 252.

[258] In plants also reversion forms show sterility in different degrees. Mr. Darwin has called my attention to the fact that the peloric (symmetrical) flowers which occasionally appear as atavistic forms in _Corydalis solida_ are partly sterile and partly fertile. That in other causes of sterility, and above all by bastardizing, the reproductive power is lost in the most varying degrees, has been known since the celebrated observations of Kölreuter and Gärtner. [Eng. ed. An Orchid (_Catasetum tridentatum_) has the sexes separate, and the male flowers (_Myanthus barbatus_) differ considerably from the female (_Monachanthus viridis_); besides these, there occurs a form with bisexual flowers which must be considered as a reversion (_Cat. tridentatum_) and _this is always sterile_. Darwin, “Fertilization of Orchids,” 2nd ed. p. 199.]

[259] As we do not know the origin of the “Paris Axolotl” I must restrict myself in the following remarks to _Siredon Mexicanus_ (Shaw).

[260] Mühlenpfordt, “Versuch einer getreuen Schilderung der Republik Mejico,” Hanover, 1844, vol. ii. p. 252.

[261] [The specific gravity of sea water (Atlantic), according to the determinations of Mr. Buchanan on board the “Challenger,” at 15.56° C. varies from 1.0278 to 1.0240. That of the water of the Dead Sea is 1.17205.--Watts’ “Dict. of Chemistry,” vol. v., table, p. 1017. R.M.]

[262] _Loc. cit._ p. 252.

[263] “Über die specifische Verschiedenheit des gefleckten und des schwarzen Erdsalamanders oder Molchs, und der höchst merkwürdigen, ganz eigenthümlichen Fortpflanzungsweise des Letzteren.” Isis, Jahrg. 1833, p. 527.

[264] The experiments referred to have not been made known; I am indebted for them to a written communication kindly furnished by an esteemed colleague.

[265] See Mühlenpfordt’s work already quoted, vol. i.

[266] In the province of botany such a case has already been made known by Fritz Müller (Botan. Zeitung, 1869, p. 226; 1870, p. 149). I may be here permitted to quote a passage from the letter in which Dr. Müller calls attention to this interesting discovery. “As a proof of the possibility that a reversion form can again become a persistent character in a species or in the allied form of a particular district, I may refer you to an _Epidendrum_ of the island of Santa Catharina. In all Orchids (with the exception of _Cypripedium_) only one anther is developed; in very rare cases well-formed anthers appear as reversions among the aborted lateral anthers of the inner whorl. In the _Epidendrum_ mentioned, these are however _always present_.”

[267] [This species is interesting as being ovoviviparous, the young passing through the branchiate stage within the body of the mother. Some experiments, which were partially successful, were made by Fräulein v. Chauvin with a view to solve the question whether the branchiate stage could be prolonged by taking the larvæ directly from the mother before birth and keeping them in water. See “Zeit. für wissen. Zoo.” vol. xxix., p. 324. R.M.]

[268] See Fatiot, “Les Reptiles et les Batraciens de la haute Engadine.” Geneva, 1873.