The Variation of Animals and Plants under Domestication Volume I Part 24

Birds of all kinds which present many distinct races are valued as pets or ornaments; no one makes a pet of the goose; the name, indeed, in more languages than one, is a term of reproach. The goose is valued for its size and flavour, for the whiteness of its feathers which adds to their value, and for its prolificness and tameness. In all these points the goose differs from the wild parent-form; and these are the points which have been selected. Even in ancient times the Roman gourmands valued the liver of the WHITE goose; and Pierre Belon (8/32. 'L'Hist. de la Nature des Oiseaux' par P. Belon 1555 page 156. With respect to the livers of white geese being preferred by the Romans see Isid. Geoffroy St.-Hilaire 'Hist. Nat. Gen.'

tome 3 page 58.) in 1555 speaks of two varieties, one of which was larger, more fecund, and of a better colour than the other; and he expressly states that good managers attended to the colour of their goslings, so that they might know which to preserve and select for breeding.

THE PEAc.o.c.k.

This is another bird which has hardly varied under domestication, except in sometimes being white or piebald. Mr. Waterhouse carefully compared, as he informs me, skins of the wild Indian and domestic bird, and they were identical in every respect, except that the plumage of the latter was perhaps rather thicker. Whether our birds are descended from those introduced into Europe in the time of Alexander, or have been subsequently imported, is doubtful. They do not breed very freely with us, and are seldom kept in large numbers,--circ.u.mstances which would greatly interfere with the gradual selection and formation of new breeds.

There is one strange fact with respect to the peac.o.c.k, namely, the occasional appearance in England of the "j.a.panned" or "black-shouldered"

kind. This form has lately been named on the high authority of Mr. Sclater as a distinct species, viz. Pavo nigripennis, which he believes will hereafter be found wild in some country, but not in India, where it is certainly unknown. The males of these j.a.panned birds differ conspicuously from the common peac.o.c.k in the colour of their secondary wing-feathers, scapulars, wing-coverts, and thighs, and are I think more beautiful; they are rather smaller than the common sort, and are always beaten by them in their battles, as I hear from the Hon. A.S.G. Canning. The females are much paler coloured than those of the common kind. Both s.e.xes, as Mr. Canning informs me, are white when they leave the egg, and they differ from the young of the white variety only in having a peculiar pinkish tinge on their wings. These j.a.panned birds, though appearing suddenly in flocks of the common kind, propagate their kind quite truly. Although they do not resemble the hybrids which have been raised between P. cristatus and muticus, nevertheless they are in some respects intermediate in character between these two species; and this fact favours, as Mr. Sclater believes, the view that they form a distinct and natural species. (8/33. Mr. Sclater on the black-shouldered peac.o.c.k of Latham 'Proc. Zoolog. Soc.' April 24, 1860. Mr. Swinhoe at one time believed, 'Ibis' July 1868, that this kind of peafowl was found wild in Cochin China, but he has since informed me that he feels very doubtful on this head.)

On the other hand, Sir H. Heron states (8/34. 'Proc. Zoolog. Soc.' April 14, 1835.) that this breed suddenly appeared within his memory in Lord Brownlow's large stock of pied, white, and common peac.o.c.ks. The same thing occurred in Sir J. Trevelyan's flock composed entirely of the common kind, and in Mr. Thornton's stock of common and pied peac.o.c.ks. It is remarkable that in these two latter instances the black-shouldered kind, though a smaller and weaker bird, increased, "to the extinction of the previously existing breed." I have also received through Mr. Sclater a statement from Mr. Hudson Gurney that he reared many years ago a pair of black-shouldered peac.o.c.ks from the common kind; and another ornithologist, Prof. A. Newton, states that, five or six years ago, a female bird, in all respects similar to the female of the black-shouldered kind, was produced from a stock of common peac.o.c.ks in his possession, which during more than twenty years had not been crossed with birds of any other strain. Mr. Jenner Weir informs me that a peac.o.c.k at Blackheath whilst young was white, but as it became older gradually a.s.sumed the characters of the black-shouldered variety; both its parents were common peac.o.c.ks. Lastly, Mr. Canning has given a case of a female of this same variety appearing in Ireland in a flock of the ordinary kind. (8/35. 'The Field' May 6, 1871. I am much indebted to Mr. Canning for information with respect to his birds.) Here, then, we have seven well authenticated cases in Great Britain of j.a.panned birds, having suddenly appeared within recent times in flocks of the common peafowl. This variety must also have formerly appeared in Europe, for Mr. Canning has seen an old picture, and another is referred to in the 'Field,' with this variety represented. These facts seem to me to indicate that the j.a.panned peac.o.c.k is a strongly marked variety or "sport," which tends at all times and in many places to reappear. This view is supported by the young being at first white like the young of the white breed, which is undoubtedly a variation.

If, on the other hand, we believe the j.a.panned peac.o.c.k to be a distinct species, we must suppose that in all the above cases the common breed had at some former period been crossed by it, but had lost every trace of the cross; yet that the offspring of these birds suddenly and completely reacquired through reversion the characters of P. nigripennis. I have heard of no other such case in the animal or vegetable kingdom. To perceive the full improbability of such an occurrence, we may suppose that a breed of dogs had been crossed at some former period with a wolf, but had lost every trace of the wolf-like character, yet that the breed gave birth in seven instances in the same country, within no great length of time, to a wolf perfect in every character; and we must further suppose that in two of the cases, the newly produced wolves afterwards spontaneously increased to such an extent as to lead to the extinction of the parent breed of dogs. So remarkable a bird as the P. nigripennis, when first imported, would have realised a large price; it is therefore improbable that it should have been silently introduced and its history subsequently lost. On the whole the evidence seems to me, as it did to Sir R. Heron, to be decisive in favour of the j.a.panned or black-shouldered breed being a variation, induced by some unknown cause. On this view, the case is the most remarkable one ever recorded of the abrupt appearance of a new form, which so closely resembles a true species that it has deceived one of the most experienced of living ornithologists.

THE TURKEY.

It seems fairly well established by Mr. Gould (8/36. 'Proc. Zoolog. Soc.'

April 8, 1856 page 61. Prof. Baird believes (as quoted in Tegetmeier 'Poultry Book' 1866 page 269) that our turkeys are descended from a West Indian species now extinct. But besides the improbability of a bird having long ago become extinct in these large and luxuriant islands, it appears (as we shall presently see) that the turkey degenerates in India, and this fact indicates that it was not aboriginally an inhabitant of the lowlands of the tropics.), that the turkey, in accordance with the history of its first introduction, is descended from a wild Mexican form, which had been domesticated by the natives before the discovery of America, and which is now generally ranked as a local race, and not as a distinct species.

However this may be, the case deserves notice because in the United States wild male turkeys sometimes court the domestic hens, which are descended from the Mexican form, "and are generally received by them with great pleasure." (8/37. Audubon 'Ornithological Biography' volume 1 1831 pages 4- 13; and 'Naturalist's Library' volume 14 'Birds' page 138.) Several accounts have likewise been published of young birds, reared in the United States from the eggs of the wild species, crossing and commingling with the common breed. In England, also, this same species has been kept in several parks; from two of which the Rev. W.D. Fox procured birds, and they crossed freely with the common domestic kind, and during many years afterwards, as he informs me, the turkeys in his neighbourhood clearly showed traces of their crossed parentage. We here have an instance of a domestic race being modified by a cross with a distinct wild race or species. F. Michaux (8/38.

F. Michaux 'Travels in N. America' 1802 English translation page 217.) suspected in 1802 that the common domestic turkey was not descended from the United States species alone, but likewise from a southern form, and he went so far as to believe that English and French turkeys differed from having different proportions of the blood of the two parent-forms.

English turkeys are smaller than either wild form. They have not varied in any great degree; but there are some breeds which can be distinguished as Norfolks, Suffolks, Whites, and Copper-coloured (or Cambridge), all of which, if precluded from crossing with other breeds propagate their kind truly. Of these kinds, the most distinct is the small, hardy, dull-black Norfolk turkey, of which the chickens are black, occasionally with white patches about the head. The other breeds scarcely differ except in colour, and their chickens are generally mottled all over with brownish-grey.

(8/39. 'Ornamental Poetry' by the Rev. E.S. Dixon 1848 page 34.) The inferior tail-coverts vary in number, and according to a German superst.i.tion the hen lays as many eggs as the c.o.c.k has feathers of this kind. (8/40. Bechstein 'Naturgesch. Deutschlands' b. 3 1793 s. 309.) Albin in 1738, and Temminck within a much later period, describe a beautiful breed, dusky-yellowish, brown above and white beneath, with a large top- knot of soft plumose feather. The spurs of the male were rudimentary. This breed has been for a long time extinct in Europe; but a living specimen has lately been imported from the east coast of Africa, which still retains the top-knot and the same general colouring and rudimentary spurs. (8/41. Mr.

Bartlett in 'Land and Water' October 31, 1868 page 233; and Mr. Tegetmeier in the 'Field' July 17, 1869 page 46.) Mr. Wilmot has described (8/42.

'Gardener's Chronicle' 1852 page 699.) a white turkey-c.o.c.k having a crest formed of "feathers about four inches long, with bare quills, and a tuft of soft white down growing at the end." Many of the young birds inherited this kind of crest, but afterwards it fell off or was pecked out by the other birds. This is an interesting case, as with care a new breed might probably have been formed; and a top-knot of this nature would have been to a certain extent a.n.a.logous to that borne by the males in several allied genera, such as Euplocomus, Lophophorus, and Pavo.

Wild turkeys, believed in every instance to have been imported from the United States, have been kept in the parks of Lords Powis, Leicester, Hill, and Derby. The Rev. W.D. Fox procured birds from the two first-named parks, and he informs me that they certainly differed a little from each other in the shape of their bodies and in the barred plumage on their wings. These birds likewise differed from Lord Hill's stock. Some of the latter kept at Oulton by Sir P. Egerton, though precluded from crossing with common turkeys, occasionally produced much paler-coloured birds, and one that was almost white, but not an albino. These half-wild turkeys, in thus differing slightly from each other, present an a.n.a.logous case with the wild cattle kept in the several British parks. We must suppose that such differences have resulted from the prevention of free intercrossing between birds ranging over a wide area, and from the changed conditions to which they have been exposed in England. In India the climate has apparently wrought a still greater change in the turkey, for it is described by Mr. Blyth (8/43.

E. Blyth 'Annals and Mag. of Nat. Hist.' 1847 volume 20 page 391.) as being much degenerated in size, "utterly incapable of rising on the wing," of a black colour, and "with the long pendulous appendages over the beak enormously developed."

THE GUINEA FOWL.

The domesticated Guinea fowl is now believed by some naturalists to be descended from the Numida ptilorhynca, which inhabits very hot, and, in parts, extremely arid districts in Eastern Africa; consequently it has been exposed in this country to extremely different conditions of life.

Nevertheless it has hardly varied at all, except in the plumage being either paler or darker-coloured. It is a singular fact that this bird varies more in colour in the West Indies and on the Spanish Main, under a hot though humid climate, than in Europe. (8/44. Roulin makes this remark in 'Mem. de divers Savans, 1'Acad. des Sciences' tome 6 1835 page 349. Mr.

Hill of Spanish Town in a letter to me describes five varieties of the Guinea fowl in Jamaica. I have seen singular pale-coloured varieties imported from Barbadoes and Demerara.) The Guinea fowl has become thoroughly feral in Jamaica and in St. Domingo (8/45. For St. Domingo see M. A. Salle, in 'Proc. Zoolog. Soc.' 1857 page 236. Mr. Hill remarks to me, in his letter, on the colour of the legs of the feral birds in Jamaica.), and has diminished in size; the legs are black, whereas the legs of the aboriginal African bird are said to be grey. This small change is worth notice on account of the often-repeated statement that all feral animals invariably revert in every character to their original type.

THE CANARY BIRD.

As this bird has been recently domesticated, namely, within the last 350 years, its variability deserves notice. It has been crossed with nine or ten other species of Fringillidae, and some of the hybrids are almost completely fertile; but we have no evidence that any distinct breed has originated from such crosses. Notwithstanding the modern domestication of the canary, many varieties have been produced; even before the year 1718 a list of twenty-seven varieties was published in France (8/46. Mr. B.P.

Brent 'The Canary, British Finches' etc. pages 21, 30.), and in 1779 a long schedule of the desired qualities was printed by the London Canary Society, so that methodical selection has been practised during a considerable period. The greater number of the varieties differ only in colour and in the markings of their plumage. Some breeds however, differ in shape, such as the hooped or bowed canaries, and the Belgian canaries with their much elongated bodies. Mr. Brent (8/47. 'Cottage Gardener' December 11, 1855 page 184: an account is here given of all the varieties. For many measurements of the wild birds, see Mr. E. Vernon Harcourt ibid December 25, 1855 page 223.) measured one of the latter and found it eight inches in length, whilst the wild canary is only five and a quarter inches long.

There are top-knotted canaries, and it is a singular fact that, if two top- knotted birds are matched, the young, instead of having very fine top- knots, are generally bald, or even have a wound on their heads. (8/48.

Bechstein 'Naturgesch. der Stubenvogel' 1840 s. 243; see s. 252 on the inherited song of Canary-birds. With respect to their baldness see also W.

Kidd 'Treatise on Song-Birds.') It would appear as if the top-knot were due to some morbid condition, which is increased to an injurious degree when two birds in this state are paired. There is a feather-footed breed, and another with a kind of frill running down the breast. One other character deserves notice from being confined to one period of life, and from being strictly inherited at the same period; namely, the wing and tail feathers in prize canaries being black, "but this colour is retained only until the first moult; once moulted, the peculiarity ceases." (8/49. W. Kidd 'Treatise on Song-Birds' page 18.) Canaries differ much in disposition and character, and in some small degree in song. They produce eggs three or four times during the year.

GOLD-FISH.

Besides mammals and birds, only a few animals belonging to the other great cla.s.ses have been domesticated; but to show that it is an almost universal law that animals, when removed from their natural conditions of life, vary, and that races can be formed when selection is applied, it is necessary to say a few words on gold-fish, bees, and silk-moths.

Gold-fish (Cyprinus auratus) were introduced into Europe only two or three centuries ago; but they have been kept in confinement from an ancient period in China. Mr. Blyth (8/50. The 'Indian Field' 1858 page 255.) suspects, from the a.n.a.logous variation of other fishes, that golden- coloured fish do not occur in a state of nature. These fishes frequently live under the most unnatural conditions, and their variability in colour, size, and in some important points of structure is very great. M. Sauvigny has described and given coloured drawings of no less than eighty-nine varieties. (8/51. Yarrell 'British Fishes' volume 1 page 319.) Many of the varieties, however, such as triple tail-fins, etc., ought to be called monstrosities; but it is difficult to draw any distinct line between a variation and a monstrosity. As gold-fish are kept for ornament or curiosity, and as "the Chinese are just the people to have secluded a chance variety of any kind, and to have matched and paired from it" (8/52.

Mr. Blyth in the 'Indian Field' 1858 page 255.), it might have been predicted that selection would have been largely practised in the formation of new breeds; and this is the case. In an old Chinese work it is said that fish with vermilion scales were first raised in confinement during the Sung dynasty (which commenced A.D. 960), "and now they are cultivated in families everywhere for the sake of ornament." In another and more ancient work, it is said that "there is not a household where the gold-fish is not cultivated, in RIVALRY as to its colour, and as a source of profit," etc.

(8/53. W.F. Mayers 'Chinese Notes and Queries' August 1868 page 123.) Although many breeds exist, it is a singular fact that the variations are often not inherited. Sir R. Heron (8/54. 'Proc. Zoolog. Soc.' May 25, 1842.) kept many of these fishes, and placed all the deformed ones, namely, those dest.i.tute of dorsal fins and those furnished with a double a.n.a.l fin, or triple tail, in a pond by themselves; but they did "not produce a greater proportion of deformed offspring than the perfect fishes."

Pa.s.sing over an almost infinite diversity of colour, we meet with the most extraordinary modifications of structure. Thus, out of about two dozen specimens bought in London, Mr. Yarrell observed some with the dorsal fin extending along more than half the length of the back: others with this fin reduced to only five or six rays: and one with no dorsal fin. The a.n.a.l fins are sometimes double, and the tail is often triple. This latter deviation of structure seems generally to occur "at the expense of the whole or part of some other fin (8/55. Yarrell 'British Fishes' volume 1 page 319.); but Bory de Saint-Vincent (8/56. 'Dict. Cla.s.s. d'Hist. Nat.' tome 5 page 276.) saw at Madrid gold-fish furnished with a dorsal fin and a triple tail. One variety is characterised by a hump on its back near the head; and the Rev.

L. Jenyns (Blomefield) (8/57. 'Observations in Nat. Hist.' 1846 page 211.

Dr. Gray has described in 'Annals and Mag. of Nat. Hist.' 1860 page 151 a nearly similar variety but dest.i.tute of a dorsal fin.) has described a most singular variety, imported from China, almost globular in form like a Diodon, with "the fleshy part of the tail as if entirely cut away? the caudal fin being set on a little behind the dorsal and immediately above the a.n.a.l." In this fish the a.n.a.l and caudal fins were double; the a.n.a.l fin being attached to the body in a vertical line: the eyes also were enormously large and protuberant.

HIVE-BEES.

Bees have been domesticated from an ancient period; if indeed their state can be considered one of domestication, for they search for their own food, with the exception of a little generally given to them during the winter.

Their habitation is a hive instead of a hole in a tree. Bees, however, have been transported into almost every quarter of the world, so that climate ought to have produced whatever direct effect it is capable of producing.

It is frequently a.s.serted that the bees in different parts of Great Britain differ in size, colour, and temper; and G.o.dron (8/58. 'De l'Espece' 1859 page 459. With respect to the bees of Burgundy see M. Gerard, art. 'Espece'

in 'Dict. Univers. d'Hist. Nat.') says that they are generally larger in the south than in other parts of France; it has also been a.s.serted that the little brown bees of High Burgundy, when transported to La Bresse become large and yellow in the second generation. But these statements require confirmation. As far as size is concerned, it is known that bees produced in very old combs are smaller, owing to the cells having become smaller from the successive old coc.o.o.ns. The best authorities (8/59. See a discussion on this subject, in answer to a question of mine, in 'Journal of Horticulture' 1862 pages 225-242; also Mr. Bevan Fox in ditto 1862 page 284) concur that, with the exception of the Ligurian race or species, presently to be mentioned, distinct breeds do not exist in Britain or on the Continent. There is, however, even in the same stock, some variability in colour. Thus, Mr. Woodbury states (8/60. This excellent observer may be implicitly trusted; see 'Journal of Horticulture' July 14, 1863 page 39.) that he has several times seen queen bees of the common kind annulated with yellow-like Ligurian queens, and the latter dark-coloured like common bees.

He has also observed variations in the colour of the drones, without any corresponding difference in the queens or workers of the same hive. The great apiarian, Dzierzon, in answer to my queries on this subject, says (8/61. 'Journal of Horticulture' September 9, 1862 page 463; see also Herr Kleine on same subject November 11 page 643, who sums up, that, though there is some variability in colour, no constant or perceptible differences can be detected in the bees of Germany.), that in Germany bees of some stocks are decidedly dark, whilst others are remarkable for their yellow colour. Bees also seem to differ in habits in different districts, for Dzierzon adds, "If many stocks with their offspring are more inclined to swarm, whilst others are richer in honey, so that some bee-keepers even distinguish between swarming and honey-gathering bees, this is a habit which has become second nature, caused by the customary mode of keeping the bees and the pasturage of the district. For example, what a difference in this respect one may perceive to exist between the bees of the Luneburg heath and those of this country!"..."Removing an old queen and subst.i.tuting a young one of the current year is here an infallible mode of keeping the strongest stock from swarming and preventing drone-breeding; whilst the same means if adopted in Hanover would certainly be of no avail." I procured a hive full of dead bees from Jamaica, where they have long been naturalised, and, on carefully comparing them under the microscope with my own bees, I could detect not a trace of difference.

This remarkable uniformity in the hive-bee, wherever kept, may probably be accounted for by the great difficulty, or rather impossibility, of bringing selection into play by pairing particular queens and drones, for these insects unite only during flight. Nor is there any record, with a single partial exception, of any person having separated and bred from a hive in which the workers presented some appreciable difference. In order to form a new breed, seclusion from other bees would, as we now know, be indispensable; for since the introduction of the Ligurian bee into Germany and England, it has been found that the drones wander at least two miles from their own hives, and often cross with the queens of the common bee.

(8/62. Mr. Woodbury has published several such accounts in 'Journal of Horticulture' 1861 and 1862.) The Ligurian bee, although perfectly fertile when crossed with the common kind, is ranked by most naturalists as a distinct species, whilst by others it is ranked as a variety: but this form need not here be noticed, as there is no reason to believe that it is the product of domestication. The Egyptian and some other bees are likewise ranked by Dr. Gerstacker (8/63. 'Annals and Mag. of Nat. Hist.' 3rd series volume 11 page 339.) but not by other highly competent judges, as geographical races; he grounds his conclusion in chief part on the fact that in certain districts, as in the Crimea and Rhodes, they vary so much in colour, that the several geographical races can be closely connected by intermediate forms.

I have alluded to a single instance of the separation and preservation of a particular stock of bees. Mr. Lowe (8/64. 'The Cottage Gardener' May 1860 page 110; and ditto in 'Journal of Hort.' 1862 page 242.) procured some bees from a cottager a few miles from Edinburgh, and perceived that they differed from the common bee in the hairs on the head and thorax being lighter coloured and more profuse in quant.i.ty. From the date of the introduction of the Ligurian bee into Great Britain we may feel sure that these bees had not been crossed with this form. Mr. Lowe propagated this variety, but unfortunately did not separate the stock from his other bees, and after three generations the new character was almost completely lost.

Nevertheless, as he adds, "a great number of the bees still retain traces, though faint, of the original colony." This case shows us what could probably be effected by careful and long-continued selection applied exclusively to the workers, for, as we have seen, queens and drones cannot be selected and paired.

SILK-MOTHS.

These insects are in several respects interesting to us, more especially because they have varied largely at an early period of life, and the variations have been inherited at corresponding periods. As the value of the silk-moth depends entirely on the coc.o.o.n, every change in its structure and qualities has been carefully attended to, and races differing much in the coc.o.o.n, but hardly at all in the adult state, have been produced. With the races of most other domestic animals, the young resemble each other closely, whilst the adults differ much.

It would be useless, even if it were possible, to describe all the many kinds of silkworms. Several distinct species exist in India and China which produce useful silk, and some of these are capable of freely crossing with the common silk-moth, as has been recently ascertained in France. Captain Hutton (8/65. 'Transact. Entomolog. Soc.' 3rd series volume 3 pages 143-173 and pages 295-331.) states that throughout the world at least six species have been domesticated; and he believes that the silk-moths reared in Europe belong to two or three species. This, however, is not the opinion of several capable judges who have particularly attended to the cultivation of this insect in France; and hardly accords with some facts presently to be given.

The common silk-moth (Bombyx mori) was brought to Constantinople in the sixth century, whence it was carried into Italy, and in 1494 into France.

(8/66. G.o.dron 'De l'Espece' 1859 tome 1 page 460. The antiquity of the silkworm in China is given on the authority of Stanislas Julien.) Everything has been favourable for the variation of this insect. It is believed to have been domesticated in China as long ago as 2700 B.C. It has been kept under unnatural and diversified conditions of life, and has been transported into many countries. There is reason to believe that the nature of the food given to the caterpillar influences to a certain extent the character of the breed. (8/67. See the remarks of Prof. Westwood, Gen.

Hea.r.s.ey and others at the meeting of the Entomolog. Soc. of London July 1861.) Disuse has apparently aided in checking the development of the wings. But the most important element in the production of the many now existing, much modified races, no doubt has been the close attention which has long been applied in many countries to every promising variation. The care taken in Europe in the selection of the best coc.o.o.ns and moths for breeding is notorious (8/68. See for instance M. A. de Quatref.a.ges 'Etudes sur les Maladies actuelles du Ver a Soie' 1859 page 101.), and the production of eggs is followed as a distinct trade in parts of France. I have made inquiries through Dr. Falconer, and am a.s.sured that in India the natives are equally careful in the process of selection. In China the production of eggs is confined to certain favourable districts, and the raisers are precluded by law from producing silk, so that their whole attention may be necessarily given up to this one object. (8/69. My authorities for the statements will be given in the chapter on Selection.)

[The following details on the differences between the several breeds are taken, when not stated to the contrary, from M. Robinet's excellent work (8/70. 'Manuel de l'Educateur de Vers a Soie' 1848.), which bears every sign of care and large experience. The EGGS in the different races vary in colour, in shape (being round, elliptic or oval), and in size. The eggs laid in June in the south of France, and in July in the central provinces, do not hatch until the following spring; and it is in vain, says M.

Robinet, to expose them to a temperature gradually raised, in order that the caterpillar may be quickly developed. Yet occasionally, without any known cause, batches of eggs are produced, which immediately begin to undergo the proper changes, and are hatched in from twenty to thirty days.

From these and some other a.n.a.logous facts it may be concluded that the Trevoltini silkworms of Italy, of which the caterpillars are hatched in from fifteen to twenty days, do not necessarily form, as has been maintained, a distinct species. Although the breeds which live in temperate countries produce eggs which cannot be immediately hatched by artificial heat, yet when they are removed to and reared in a hot country they gradually acquire the character of quick development, as in the Trevoltini races. (8/71. Robinet ibid pages 12, 318. I may add that the eggs of N.

American silkworms taken to the Sandwich Islands produced moths at very irregular periods; and the moths thus raised yielded eggs which were even worse in this respect. Some were hatched in ten days, and others not until after the lapse of many months. No doubt a regular early character would ultimately have been acquired. See review in 'Athenaeum' 1844 page 329 of J. Jarves 'Scenes in the Sandwich Islands.')

CATERPILLARS.

These vary greatly in size and colour. The skin is generally white, sometimes mottled with black or grey, and occasionally quite black. The colour, however, as M. Robinet a.s.serts, is not constant, even in perfectly pure breeds; except in the race tigree, so called from being marked with transverse black stripes. As the general colour of the caterpillar is not correlated with that of the silk (8/72. 'The Art of rearing Silkworms'

translated from Count Dandolo 1825 page 23.), this character is disregarded by cultivators, and has not been fixed by selection. Captain Hutton, in the paper before referred to, has argued with much force that the dark tiger- like marks, which so frequently appear during the later moults in the caterpillars of various breeds, are due to reversion; for the caterpillars of several allied wild species of Bombyx are marked and coloured in this manner. He separated some caterpillars with the tiger-like marks, and in the succeeding spring (pages 149, 298) nearly all the caterpillars reared from them were dark-brindled, and the tints became still darker in the third generation. The moths reared from these caterpillars (8/73.

'Transact. Ent. Soc.' ut supra pages 153, 308.) also became darker, and resembled in colouring the wild B. huttoni. On this view of the tiger-like marks being due to reversion, the persistency with which they are transmitted is intelligible.

Several years ago Mrs. Whitby took great pains in breeding silkworms on a large scale, and she informed me that some of her caterpillars had dark eyebrows. This is probably the first step in reversion towards the tiger- like marks, and I was curious to know whether so trifling a character would be inherited. At my request she separated in 1848 twenty of these caterpillars, and having kept the moths separate, bred from them. Of the many caterpillars thus reared, "every one without exception had eyebrows, some darker and more decidedly marked than the others, but ALL had eyebrows more or less plainly visible." Black caterpillars occasionally appear amongst those of the common kind, but in so variable a manner, that, according to M. Robinet, the same race will one year exclusively produce white caterpillars, and the next year many black ones; nevertheless, I have been informed by M. A. Bossi of Geneva, that, if these black caterpillars are separately bred from, they reproduce the same colour; but the coc.o.o.ns and moths reared from them do not present any difference.

The caterpillar in Europe ordinarily moults four times before pa.s.sing into the coc.o.o.n stage; but there are races "a trois mues," and the Trevoltini race likewise moults only thrice. It might have been thought that so important a physiological difference would not have arisen under domestication; but M. Robinet (8/74. Robinet ibid page 317.) states that, on the one hand, ordinary caterpillars occasionally spin their coc.o.o.ns after only three moults, and, on the other hand, "presque toutes les races a trois mues, que nous avons experimentees, ont fait quatre mues a la seconde ou a la troisieme annee, ce qui semble prouver qu'il a suffi de les placer dans des conditions favorables pour leur rendre une faculte qu'elles avaient perdue sous des influences moins favorables."

COc.o.o.nS.

The caterpillar in changing into the coc.o.o.n loses about 50 per cent of its weight; but the amount of loss differs in different breeds, and this is of importance to the cultivator. The coc.o.o.n in the different races presents characteristic differences; being large or small;--nearly spherical with no constriction, as in the Race de Loriol, or cylindrical, with either a deep or slight constriction in the middle; with the two ends, or with one end alone, more or less pointed. The silk varies in fineness and quality, and in being nearly white, but of two tints, or yellow. Generally the colour of the silk is not strictly inherited: but in the chapter on Selection I shall give a curious account how, in the course of sixty-five generations, the number of yellow coc.o.o.ns in one breed has been reduced in France from one hundred to thirty-five in the thousand. According to Robinet, the white race, called Sina, by careful selection during the last seventy-five years, "est arrivee a un tel etat de purete, qu'on ne voit pas un seul cocon jaune dans des millions de cocons blancs." (8/75. Robinet ibid pages 306-317.) Coc.o.o.ns are sometimes formed, as is well known, entirely dest.i.tute of silk, which yet produce moths; unfortunately Mrs. Whitby was prevented by an accident from ascertaining whether this character would prove hereditary.

ADULT STAGE.

I can find no account of any constant difference in the moths of the most distinct races. Mrs. Whitby a.s.sured me that there was none in the several kinds bred by her; and I have received a similar statement from the eminent naturalist, M. de Quatref.a.ges. Captain Hutton also says (8/76. 'Transact.