V 1 (,2$ y? 5b $,1 /"<* — J?3 THE VARIATION OF ANIMALS AND PLANTS UNDER DOMESTICATION. Bt CHAELES DARWIN, M.A., F.R.S., &c. SECOND EDITION, REVISED. FIFTH THOUSAND. IN TWO VOLUMES.— Vol. II WITH ILLUSTRATIONS. LONDON: JOHN MURRAY, ALBEMARLE STREET. 1885. The rignt of Translation is reserved. BY THE SAME AUTHOR. A NATURALIST'S VOYAGE ROUND THE WORLD; or, A Journal of Researches ikto the Natural History and Geology of the Countries visited during the Voyage of H.M.S. ' Beagle,' under the com- and of Captain FitzRoy, R.N. Sixteenth Thousand. 9s. Murrat. ORIGIN OF SPECIES BY MEANS OF NATURAL SELEC- TION ; or, The Preservation of Favoured Races in the Struggle fok Lifl ^Twenty-eighth Thousand. 7s 6d. Murray. VARIOUS CONTRIVANCES BY WHICH BRITISH AND FOREIGN ORCHIDS ARE FERTILIZED BY INSECTS. Fourth Thousand. With Woodcuts. 9s. Murray. VARIATION OF ANIMALS AND PLANTS UNDER DO- MESTICATION. With Illustrations. Fifth Thousand. 2 vols. l*s. Murray. DESCENT OF MAN, AND SELECTION IN RELATION TO SEX. With Illustrations. Nineteenth Thousand. 9s. Murray. EXPRESSION OF THE EMOTIONS IN MAN AND ANI- MALS. With Illustrations. Ninth Thousand, 12s. Mursjay. INSECTIVOROUS PLANTS. With Illustrations. Fourth Thou- sand Us Murray. MOVEMENTS AND HABITS OF CLIMBING PLANTS. With Illustrations. Third Thousand. 6s. Murray. EFFECTS OF CROSS AND SELF-FERTILIZATION IN THE VEGETABLE KINGDOM. Third Thousand. 12s. Murray. DIFFERENT FORMS OF FLOWERS ON PLANTS OF THE SAME SPECIFS. Third Thousmd. 10s. 6d. Murray. LIFE OF ERASMUS DARWIN. By Ersest Krause. With Preliminary Notice. 1.-. 6d. .Murray. POWER OF MOVEMENT IN PLANTS. With Woodcuts. Second Thousand. 15s. Murray. FORMATION OF VEGETABLE MOULD THROUGH THE ACTION OF WORMS, with Observations ou their Habits. Ninth Thousand. 9s_ Murray. ON THE STRUCTURE AND DISTRIBUTION OF CORAL KEEFS. Second Edition, revised. Smith, Elder, & Co. GEOLOGICAL OBSERVATIONS ON THE VOLCANIC ISLANDS AND PAKTS OF SOUTH AMERICA, visited during the Voyage of H.M.S. ' Beagle.' Second Edition. Smith, Elder, & Co. A MONOGRAPH OF THE CIRRIPEDIA. With numerous Illustrations. 2 vols. Ray Society. Hardwicke. A MONOGRAPH OF THE FOSSIL LEPAD1D.E, OR PEDUNCULATED CIllRil'LDS OF GREAT BRITAIN. Palsontographical Society. A MONOGRAPH OF THE FOSSIL BALANID.E AND VERRUOID.E OF GREAT BRITAIN. Pal.eo.siograi'hical Society. FACTS AND ARGUMENTS FOR DARWIN. By Fritz MOllk.r. From the German, with Additions by the Auinor. Tran^atJd by W. S. Dallas, F.L.S. With Illustrations. 6s. MuiiKAr. LONDON : PRINTED BY WILLIAM CLOWES AND SONS, LIMITED, SIAJIEOSD sTBEfir AN D UWRLUj JSiipiS. AUG 1 9 1957 CONTENTS. CHAPTER XIII. inheritance, continued — reversion or atavism. DIFFERENT FORMS OF REVERSION — IN PURE OR UNCROSSED BREEDS, AS IN PIGEONS, FOWLS, HORNLESS CATTLE AND SHEEP, IN CULTIVATED PLANTS — REVERSION IN FERAL ANIMALS AND PLANTS — REVERSION IN CROSSED VARIETIES AND SPECIES — REVERSION THROUGH BUD- PROPAGATION, AND BY SEGMENTS IN THE SAME FLOWER OR FRUIT — LN DIFFERENT PARTS OF THE BODY IN THE SAME ANIMAL — THE ACT OF CROSSING A DIRECT CAUSE OF REVERSION, VARIOUS CASES OF, WITH INSTINCTS— OTHER PROXIMATE CAUSES OF RE- VERSION— LATENT CHARACTERS — SECONDARY SEXUAL CHARACTERS — UNEQUAL DEVELOPMENT OF THE TWO SIDES OF THE BODY — APPEARANCE WITH ADVANCING AGE OF CHARACTERS DERIVE'.. FROM A CROSS — THE GERM, WITH ALL ITS LATENT CHARACTERS, A WONDERFUL OBJECT — MONSTROSITIES — PELORIC FLOWERS DUE IN some cases to reversion Pages 1-36 CHAPTER XIV. inheritance, continued — fixedness of character — PREPOTENCY — SEXUAL LIMITATION — CORRESPONDENCE OF AGE. FIXEDNESS OF CHARACTER APPARENTLY NOT DUE TO ANTIQUITY OF INHERITANCE — PREPOTENCY OF TRANSMISSION IN INDIVIDUALS OF THE SAME FAMILY, IN CROSSED BREEDS AND SPECIES ; OFTEN STRONGER IN ONE SEX THAN THE OTHER; SOMETIMES DUE TO THE SAME CHARACTER BELNG PRESENT AND VISIBLE IN ONE BREED AND LATENT IN THE OTHER — INHERITANCE AS LIMITED BY SEX — iv CONTENTS. NEWLY-ACQUIRED CHARACTERS IN OUR DOMESTICATED ANIMALS OFTEN TRANSMITTED BY ONE SEX ALONE, SOMETIMES LOST BY ONE SEX ALONE — INHERITANCE AT CORRESPONDING PERIODS OF LIFE — THE IMPORTANCE OF THE PRINCIPLE WITH RESPECT TO EMBRY- OLOGY ; AS EXHIBITED IN DOMESTICATED ANIMALS ; AS EXHIBITED IN THE APPEARANCE AND DISAPPEARANCE OF INHERITED DIS- EASES; SOMETIMES SUPERVENING EARLIER IN THE CHILD THAN IN THE PARENT — SUMMARY OF THE THREE PRECEDING CHAPTERS. Pages 37-61 CHAPTER XV. ON CROSSING. FREE INTERCROSSING OBLITERATES THE DIFFERENCES BETWEEN ALLIED BREEDS — WHEN THE NUMBERS OF TWO COMMINGLING BREEDS ARE UNEQUAL, ONE ABSORBS THE OTHER — THE RATE OF ABSORPTION DETERMINED BY PREPOTENCY OF TRANSMISSION, BY THE CON- DITIONS OF LIFE, AND BY NATURAL SELECTION — ALL ORGANIC BEINGS OCCASIONALLY INTERCROSS ; APPARENT EXCEPTIONS — ON CERTAIN CHARACTERS INCAPABLE OF FUSION ; CHIEFLY OR EX- CLUSIVELY THOSE WHICH HAVE SUDDENLY APPEARED IN THE IN- DIVIDUAL— ON THE MODIFICATION OF OLD RACES, AND THE FORMATION OF NEW RACES, BY CROSSING SOME CROSSED RACES HAVE BRED TRUE FROM THEIR FIRST PRODUCTION ON THE CROSS- ING OF DISTINCT SPECIES IN RELATION TO THE FORMATION OF DOMESTIC RACES 62-77 CHAPTER XVI. CAUSES WHICH INTERFERE WITH THE FREE CROSSING OF VARIETIES — INFLUENCE OF DOMESTICATION ON FER- TILITY. DIFFICULTIES IN JUDGING OF THE FERTILITY OF VARIETIES WHEN CROSSED — VARIOUS CAUSES WHICH KEEP VARIETIES DISTINCT, AS THE PERIOD OF BREEDING AND SEXUAL PREFERENCE — VARIETIES OF WHEAT SAID TO BE STERILE WHEN CROSSED — VARIETIES OF MAIZE, VERBASCUM, HOLLYHOCK, GOURDS, MELONS, AND TOBACCO CONTENTS. V RENDERED IN SOME DEGREE MUTUALLY STERILE — DOMESTICATION ELIMINATES THE TENDENCY TO STERILITY NATURAL TO SPECIES WHEN CROSSED ON THE INCREASED FERTILITY OF UNCROSSED ANIMALS AND PLANTS FROM DOMESTICATION AND CULTIVATION. Pages 78-91 CHAPTER XVII. ON THE GOOD EFFECTS OF CUOSSING, AND ON THE EVIL EFFECTS OF CLOSE INTERBEEEDING. DEFINITION OF CLOSE INTERBREEDING — AUGMENTATION OF MORBID TENDENCIES GENERAL EVIDENCE OF THE GOOD EFFECTS DERIVED FROM CROSSING, AND ON THE EVIL EFFECTS OF CLOSE INTERBREED- ING CATTLE, CLOSELY INTERBRED; HALF-WILD CATTLE LONG KEPT IN THE SAME PARKS — SHEEP — FALLOW-DEER — DOGS, RABBITS, PIGS — MAN, ORIGIN OF HIS ABHORRENCE OF INCESTUOUS MARRIAGES — FOWLS — PIGEONS — HIVE-BEES PLANTS, GENERAL CONSIDERA- TIONS ON THE BENEFITS DERIVED FROM CROSSING — MELONS, FRUIT- TREES, PEAS, CABBAGES, WHEAT, AND FOREST-TREES — ON THE INCREASED SIZE OF HYBRID PLANTS, NOT EXCLUSIVELY DUE TO THEIR STERILITY — ON CERTAIN PLANTS WHICH EITHER NORMALLY OR ABNORMALLY ARE SELF-IMPOTENT, BUT ARE FERTILE BOTH ON THE MALE AND FEMALE SIDE, WHEN CROSSED WITH DISTINCT INDIVIDUALS EITHER OF THE SAME OR ANOTHER SPECIES — CON- CLUSION ! 92-126 CHAPTER XVIII. ON THE ADVANTAGES AND DISADVANTAGES OF CHANGED CONDITIONS OF LIFE : STERILITY FROM VARIOUS CAUSES. ON THE GOOD DERIVED FROM SLIGHT CHANGES IN THE CONDITIONS OF LIFE— STERILITY FROM CHANGED CONDITIONS, IN ANIMALS, IN THEIR NATIVE COUNTRY AND IN MENAGERIES — MAMMALS, BIRDS, AND INSECTS — LOSS OF SECONDARY SEXUAL CHARACTERS AND OF INSTINCTS — CAUSES OF STERILITY — STERILITY OF DOMESTICATED ANIMALS FROM CHANGED CONDITIONS — SEXUAL INCOMPATIBILITY OF INDIVIDUAL ANIMALS — STERILITY OF PLANTS FROM CHANGED Vi CONTENTS. CONDITIONS OF LIFE — CONTABESCENCE OF THE ANTHERS — MON- STROSITIES AS A CAUSE OF STERILITY — DOUBLE FLOWERS— SEED- LESS FRUIT — STERILITY FROM THE EXCESSIVE DEVELOPMENT OF THE ORGANS OF VEGETATION— FROM LONG-CONTINUED PROPAGA- TION BY BUDS — INCIPIENT STERILITY THE PRIMARY CAUSE OF DOUBLE FLOWERS AND SEEDLESS FRUIT .. .. Pages 127-156 CHAPTER XIX. SUMMARY OF THE FOUR LAST CHAPTEES, WITH REMAKES ON HYBRIDISM. ON THE EFFECTS OF CROSSING THE INFLUENCE OF DOMESTICATION ON FERTILITY — CLOSE INTERBREEDING — GOOD AND EVIL RESULTS FROM CHANGED CONDITIONS OF LIFE — VARIETIES WHEN CROSSED NOT INVARIABLY FERTILE ON THE DIFFERENCE IN FERTILITY EE- TWEEN CROSSED SPECIES AND VARIETIES — CONCLUSIONS WITH RE- SPECT TO HYBRIDISM — LIGHT THROWN ON HYBRIDISM BY THE ILLEGITIMATE PROGENY OF HETEROSTYLED PLANTS — STERILITY OF CROSSED SPECIES DUE TO DIFFERENCES CONFINED TO THE REPRODUCTIVE SYSTEM — NOT ACCUMULATED THROUGH NATURAL SELECTION — REASONS WHY DOMESTIC VARIETIES ARE NOT MUTUALLY STERILE — TOO MUCH STRESS HAS BEEN LAID ON THE DIFFERENCE IN FERTILITY BETWEEN CROSSED SPECIES AND CROSSED VARIETIES — CONCLUSION ' 157-175 CHAPTER XX. SELECTION BY MAN. SELECTION A DIFFICULT ART — METHODICAL, UNCONSCIOUS, AND NATURAL SELECTION — RESULTS OF METHODICAL SELECTION CARE TAKEN IN SELECTION — SELECTION WITH PLANTS — SELECTION CARRIED ON BY THE ANCIENTS AND BY SEMI-CIVILISED PEOPLE UNIMPORTANT CHARACTERS OFTEN ATTENDED TO — UNCONSCIOUS SELECTION AS CIRCUMSTANCES SLOWLY CHANGE, SO HAVE OUR DOMESTICATED ANIMALS CHANGED THROUGH THE ACTION OF UNCONSCIOUS SELEC- TION— INFLUENCE OF DIFFERENT BREEDERS ON THE SAME SUB- CONTENTS. Vll VARIETY — PLANTS AS AFFECTED BY UNCONSCIOUS SELECTION — EFFECTS OF SELECTION AS SHOWN BY THE GREAT AMOUNT OF DIFFERENCE IN THE PARTS MOST VALUED BY MAN .. Pages 176-208 CHAPTER XXI. selection, continued. NATURAL SELECTION AS AFFECTING DOMESTIC PRODUCTIONS CHARAC- TERS WHICH APPEAR OF TRIFLING VALUE OFTEN OF REAL IM- PORTANCE— CIRCUMSTANCES FAVOURABLE TO SELECTION BY MAN — FACILITY IN PREVENTING CROSSES, AND THE NATURE OF THE CONDITIONS CLOSE ATTENTION AND PERSEVERANCE INDISPENSABLE — THE PRODUCTION OF A LARGE NUMBER OF INDIVIDUALS ESPE- CIALLY FAVOURABLE — WHEN NO SELECTION IS APPLIED, DISTINCT RACES ARE NOT FORMED — HIGHLY-BRED ANIMALS LIABLE TO DE- GENERATION— TENDENCY IN MAN TO CARRY THE SELECTION OF EACH CHARACTER TO AN EXTREME POINT, LEADING TO DIVERGENCE OF CHARACTER, RARELY TO CONVERGENCE — CHARACTERS CON- TINUING TO VARY IN THE SAME DIRECTION IN WHICH THEY HAVE ALREADY VARIED — DIVERGENCE OF CHARACTER WITH THE EX- TINCTION OF INTERMEDIATE VARIETIES, LEADS" TO DISTINCTNESS IN OUR DOMESTIC RACES — LIMIT TO THE POWER OF SELECTION — LAPSE OF TIME IMPORTANT — MANNER IN WHICH DOMESTIC RACES HAVE ORIGINATED— SUMMARY 209-236 CHAPTER XXII. CAUSES OF VARIABILITY. VARIABILITY DOES NOT NECESSARILY ACCOMPANY REPRODUCTION CAUSES ASSIGNED BY VARIOUS AUTHORS — INDIVIDUAL DIFFERENCES — VARIABILITY OF EVERY KIND DUE TO CHANGED CONDITIONS OF LIFE — ON THE NATURE OF SUCH CHANGES — CLIMATE, FOOD, EX- CESS OF NUTRIMENT — SLIGHT CHANGES SUFFICIENT — EFFECTS OF GRAFTING ON THE VARIABILITY OF SEEDLING-TREES — DOMESTIC PRO- DUCTIONS BECOME HABITUATED TO CHANGED CONDITIONS — ON THE ACCUMULATIVE ACTION OF CHANGED CONDITIONS — CLOSE INTER- BREEDING AND THE IMAGINATION OF THE MOTHER SUPPOSED TO Vlll CONTENTS. CAUSE VAKIABILITT — CROSSING AS A CAUSE OF THE APPEARANCE OF NEW CHARACTERS — VARIABILITY FROM THE COMMINGLING OF CHARACTERS AND FROM REVERSION — ON THE MANNER AND PERIOD OF ACTION OF THE CAUSES WHICH EITHER DIRECTLY, OR IN- DIRECTLY THROUGH THE REPRODUCTIVE SYSTEM, INDUCE VARIA- BILITY Pages 237-259 CHAPTEE XXIII. DIRECT AND DEFINITE ACTION OF THE EXTERNAL CON- DITIONS OF LIFE. SLIGHT MODIFICATIONS IN PLANTS FROM THE DEFINITE ACTION OF CHANGED CONDITIONS, IN SIZE, COLOUR, CHEMICAL PROPERTIES, AND IN THE STATE OF THE TISSUES — LOCAL DISEASES CON- SPICUOUS MODIFICATIONS FROM CHANGED CLIMATE OR FOOD, ETC. — PLUMAGE OF BIRDS AFFECTED BY PECULIAR NUTRIMENT, AND BY THE INOCULATION OF POISON — LAND-SHELLS — MODIFICATIONS OF ORGANIC BEINGS IN A STATE OF NATURE THROUGH THE DEFINITE ACTION OF EXTERNAL CONDITIONS — COMPARISON OF AMERICAN AND EUROPEAN TREES — GALLS — EFFECTS OF PARASITIC FUNGI CONSIDERATIONS OPPOSED TO THE BELIEF IN THE POTENT IN- FLUENCE OF CHANGED EXTERNAL CONDITIONS— PARALLEL SERIES OF VARIETIES — AMOUNT OF VARIATION DOES NOT CORRESPOND WITH THE DEGREE OF CHANGE IN THE CONDITIONS — BUD-VARIA- TION— MONSTROSITIES PRODUCED BY UNNATURAL TREATMENT — SUMMARY 260-282 CHAPTER XXIV. LAWS OF VARIATION — USE AND DISUSE, ETC. NISCS FORMATIVUS, OR THE CO-ORDINATING POWER OF THE ORGANISA- TION— ON THE EFFECTS OF THE INCREASED USE AND DISUSE OF ORGANS — CHANGED HABITS OF LIFE — ACCLIMATISATION WITH ANIMALS AND PLANTS — VARIOUS METHODS BY WHICH THIS CAN BE EFFECTED — ARRESTS OF DEVELOPMENT — RUDIMENTARY ORGANS. 283-310 CONTENTS. IX CHAPTER XXV. LAWS OF VARIATION, continued — CORRELATED VARIA- BILITY. EXPLANATION OF TERM CORRELATION — CONNECTED WITH DEVELOP- MENT — MODIFICATIONS CORRELATED WITH THE INCREASED OR DECREASED SIZE OF PARTS — CORRELATED VARIATION OF HOMO- LOGOUS PARTS — FEATHERED FEET IN BIRDS ASSUMING THE STRUC- TURE OF THE WINGS— CORRELATION BETWEEN THE HEAD AND THE EXTREMITIES — BETWEEN THE SKIN AND DERMAL APPENDAGES BETWEEN THE ORGANS OF SIGHT AND HEARING CORRELATED MODIFICATIONS IN THE ORGANS OF PLANTS — CORRELATED MON- STROSITIES— CORRELATION BETWEEN THE SKULL AND EARS — SKULL AND CREST OF FEATHERS — SKULL AND HORNS — CORRELATION OF GROWTH COMPLICATED BY THE ACCUMULATED EFFECTS OF NATURAL SELECTION — COLOUR AS CORRELATED WITH CONSTITUTIONAL PECU- LIARITIES Pages 311-332 CHAPTER XXVI. laws of variation, continued — summary. THE FUSION OF HOMOLOGOUS PARTS — THE VARIABILITY OF MULTIPLE AND HOMOLOGOUS PARTS — COMPENSATION OF GROWTH MECHANICAL PRESSURE— RELATIVE POSITION OF FLOWERS WITH RESPECT TO THE AXIS, AND OF SEEDS IN THE OVARY, AS INDUCING VARIA- TION— ANALOGOUS OR PARALLEL VARIETIES — SUMMARY OF THE THREE LAST CHAPTERS 333-348 CHAPTER XXVLL provisional hypothesis of pangenesis. PRELIMINARY REMARKS — FIRST PART: — THE FACTS TO BE CONNECTED UNDER A SINGLE POINT OF VIEW, NAMELY, THE VARIOUS KINDS OF REPRODUCTION — RE-GROWTH OF AMPUTATED PARTS — GRAFT- HYBRIDS — THE DIRECT ACTION OF THE MALE ELEMENT ON THE vol. n. b X CONTENTS. FEMALE— DEVELOPMENT — THE FUNCTIONAL INDEPENDENCE OF THE UNITS OF THE BODY — VARIABILITY — INHERITANCE — REVERSION. SECOND PART: STATEMENT OF THE HYPOTHESIS HOW FAR THE NECESSARY ASSUMPTIONS ARE IMPROBABLE — EXPLANATION BY AID OF THE HYPOTHESIS OF THE SEVERAL CLASSES OF FACTS SPECI- FIED IN THE FIRST PART CONCLUSION . . . . Pa^CS 349-399 CHAPTER XXVIII. CONCLUDING REMARKS. DOMESTICATION — NATURE AND CAUSES OF VARIABILITY — SELECTION — DIVERGENCE AND DISTINCTNESS OF CHARACTER EXTINCTION OF RACES — CIRCUMSTANCES FAVOURABLE TO SELECTION BY MAN — ANTIQUITY OF CERTAIN RACES — THE QUESTION WHETHER EACH ARTICULAR VARIATION HAS BEEN SPECIALLY PREORDAINED. 400-423 INDEX 429 ERRATA TO VOL. II. Page 14, four lines from bottom : for " A. moschata, Linn.," read " Cairina moschata." „ 134, last line.; for " apera," read " aperea." THE VARIATION OF ANIMALS AND PLANTS UNDER DOMESTICATION. CHAPTER XIII. INHERITANCE continued — REVERSION OR ATAVISM. DIFFERENT FORMS OF REVERSION — IN PURE OR UNCROSSED BREEDS, AS IN PIGEONS, FOWLS, HORNLESS CATTLE AND SHEEP, IN CULTIVATED PLANTS — REVERSION IN FERAL ANIMALS AND PLANTS — REVERSION LN CROSSED VARIETTES AND SPECIES — REVERSION THROUGH BUD-PROPAGATION, AND BY SEGMENTS IN THE SAME FLOWER OR FRUIT — LN DIFFERENT PARTS OF THE BODY IN THE SAME ANIMAL — THE ACT OF CROSSING A DIRECT CAUSE OF REVERSION, VARIOUS CASES OF, WITH INSTINCTS — OTHER PROXIMATE CAUSES OF REVERSION LATENT CHARACTERS — SECONDARY SEXUAL CHARACTERS — UNEQUAL DEVELOPMENT OF THE TWO SIDES OF THE BODY — APPEARANCE WITH ADVANCING AGE OF CHARACTERS DERIVED FROM A CROSS — THE GERM, WITH ALL ITS LATENT CHARACTERS. A WONDERFUL OBJECT — MONSTROSITIES — PELORIC FLOWERS DUE IN SOME CASES TO REVERSION. The great principle of inheritance to be discussed in this chapter has been recognised by agriculturists and authors of various nations, as shown by the scientific term Atavism, de- rived from atavus, an ancestor; by the English terms of Reversion, or Throwing-back ; by the French Pas-en- Arriere ; and by the German Muckschlag, or Ruckschritt. When the child resembles either grandparent more closely than its immediate parents, our attention is not much arrested, though in truth the fact is highly remarkable ; but when the child resembles some remote ancestor or some distant member in a collateral line, — and in the last case we must attribute this to the descent of all the members from a common progenitor, — we feel a just degree of astonishment. When one parent alone displaj'S some newly-acquired and generally inheritable VOL. II. B 2 INHERITANCE. Chap. XIII. character, and the offspring do not inherit it, the cause may lie in the other parent having the power of prepotent trans- mission. But when both parents are similarly characterised, and the child does not, whatever the cause may be, inherit the character in question, but resembles its grandparents, we have one of the simplest cases of reversion. We continually see another and even more simple case of atavism, though not generally included under this head, namely, when the son more closely resembles his maternal than his paternal grand- sire in some male attribute, as in any peculiarity in the beard of man, the horns of the bull, the hackles or comb of the cock\ or, as in certain diseases necessarily confined to the male sex ; for as the mother cannot possess or exhibit such male attri- butes, the child must inherit them, through her blood, from his maternal grandsire. The cases of reversion may be divided into two main classes which, however, in some instances, blend into one another ; namely, first, those occurring in a variety or race which has not been crossed, but has lost by variation some character that it formerly possessed, and which afterwards reappears. The second class includes all cases in which an individual with some distinguishable character, a race, or species, has at some former period been crossed, and a character derived from this cross, after having disappeared during one or several generations, suddenly reappears. A third class, differing only in the manner of reproduction, might be formed to include all cases of reversion effected by means of buds, and therefore independent of true or seminal generation. Perhaps even a fourth class might be instituted, to include reversions by seg- ments in the same individual flower or fruit, and in different parts of the body in the same individual animal as it grows old. But the two first main classes will be sufficient for our purpose. Reversion to lost Characters by pure or uncrossed forms. — Striking instances of this first class of cases were given in the sixth chapter, namely, of the occasional reappearance, in variously-coloured breeds of the pigeon, of blue birds with all the marks characteristic of the wild Columba livia. Similar Chap. XIII. REVERSION. o cases were given in the case of the fowl. With the common ass, as the legs of the wild progenitor are almost always striped, we may feel assured that the occasional appearance of such stripes in the domestic animal is a case of simple reversion. But I shall be compelled to refer again to these cases, and therefore here pass them over. The aboriginal species from which our domesticated cattle and sheep are descended, no doubt possessed horns ; but several hornless breeds are now well established. Yet in these — for instance, in Southdown sheep — " it is not unusual to find among the male lambs some with small horns." The horns, which thus occasionally reappear in other polled breeds, either " grow to the full size," or are curiously attached to the skin alone and hang " loosely down, or drop off." l The Galloways and Suffolk cattle have been hornless for the last 100 or 150 years, but a horned calf, with the horn often loosely attached, is occasionally produced. - There is reason to believe that sheep in their early domesti- cated condition were " brown or dingy black ; " but even in the time of David certain flocks were spoken of as white as snow. During the classical period the sheep of Spain are described by several ancient authors as being black, red, or tawny.3 At the present day, notwithstanding the great car-. which is taken to prevent it, particoloured lambs and some entirely black are occasionally, or even frequently, dropped by our most highly improved and valued breeds, such as the Southdowns. iSince the time of the famous Bakewell, during the last century, the Leicester sheep have been bred with the most scrupulous care ; yet occasionally grey-faced, or black- spotted, or wholly black lambs appear.4 This occurs still more frequently with the less improved breeds, such as the Xorfolks.5 As bearing on this tendency in sheep to revert to dark colours, I may state (though in doing so I trench on 1 Youatt on Sheep, pp. 20, 234. 145. The same fact of loose horns oc- 4 I have been informed of this fact casionally appearing in hornless breels through the Rev. W. D. Fox, on tiit has been observed in Germany ; excellent authority of Mr. Wilmot : Bechstein, ' Xaturgesch. Deutsch- see, also, remarks on this subject ii iands.' b. i. s. 362. an article in the 'Quarterly Review. ' * Youatt on Cattle, pp. 155, 174. 1849, p. 395. * Youatt on Sheep, 1838, pp. 17, 5 Youatt, pp. 19, 234. B 2 4 INHERITANCE. Chap. XIII. the reversion of crossed breeds, and likewise on the subject of prepotency) that the Rev. W. D. Fox was informed that seven white Southdown ewes were put to a so-called Spanish ram, which had two small black spots on his sides, and they pro- duced thirteen lambs, all perfectly black. Mr. Fox believes that this ram belonged to a breed which he has himself kept, and which is always spotted with black and white ; and he finds that Leicester sheep crossed by rams of this breed always produce black lambs : he has gone on recrossing these crossed sheep with pure white Leicesters during three successive generations, but always with the same result. Mr. Fox was also told by the friend from whom the spotted breed was procured, that he likewise had gone on for six or seven gene- rations crossing with white sheep, but still black lambs were invariably produced. Similar facts could be given with respect to tailless breeeds of various animals. For instance, Mr. Hewitt 6 states that chickens bred from some rumpless fowls, which were reckoned so good that they won a prize at- an exhibition, " in a consider- able number of instances were furnished with fully developed tail-feathers." On inquiry, the original breeder of these fowls stated that, from the time when he had first kept them, they had often produced fowls furnished with tails ; but that these latter would again reproduce rumpless chickens. Analogous cases of reversion occur in the vegetable king- dom ; thus '• from seeds gathered from the finest cultivated varieties of Heartsease (Viola tricolor), plants perfectly wild both in their foliage and their flowers are frequently pro- duced ;" 7 but the reversion in this instance is not to a very ancient period, for the best existing varieties of the heartsease are of comparatively modern origin. With most of our cul- tivated vegetables there is some tendency to reversion to what is known to be, or may be presumed to be, their abori- ginal state ; and this would be more evident if gardeners did not generally look over their beds of seedlings, and pull up 6 'The Poultry Book,' by Mr, much experience on this subject, ha> Tegetmeier, 1866, p. 231. likewise assured me that this some- 7 Loudon's ' Gard. Mag.,' vol. x.. times occurs 1834, p. 396- a nurseryman, with Chap. XIII. REVERSION. 5 the false plants or " rogues " as they are called. It has already been remarked, that some few seedling apples and pears generally resemble, but apparently are not identical with, the wild trees from which they are descended. In our turnip s and carrot-beds a few plants often " break " — that is', flower too soon ; and their roots are generally hard and stringy, as in the parent-species. By the aid of a little selection, carried on during a few generations, most of our cultivated plants could probably be brought back, without any great change in their conditions of life, to a wild or nearly wild condition : Mr. Buckman has effected this with the parsnip ; 9 and Mr. Hewett C. Watson, as he informs me, selected, during three generations, " the most diverging plants of Scotch kail, perhaps one of the least modified varieties of the cabbage ; and in the third generation some of the plants came very close to the forms now established in England about old castle-walls, and called indigenous." Reversion in Animals and Plants which have run ivild. — In the cases hitherto considered, the reverting animals and plants have not been exposed to any great or abrupt change in their conditions of life which could have induced this tendency ; but it is very different with animals and plants which have become feral or run wild. It has been repeatedly asserted in the most positive manner by various authors, that feral animals and plants invariably return to their primitive specific type. It is curious on what little evidence this belief rests. Many of our domesticated animals could not subsist in a wild state ; thus, the more highly improved breeds of the pigeon will not " field " or search for their own food. Sheep have never become feral, and would be destroyed by almost every beast of prey.10 In several cases we do not know the aboriginal parent-species, and cannot possibly tell 8 ' Gardener's Chron.,' 1855, p. found that they are not able to es- 777. tablish themselves ; they generally 9 Ibid., 1862, p. 721. perish from the frozen snow clinging 10 Mr. Boner speaks (' Chamois- to their wool, and they have lost the hunting,' 2nd edit., 1860, p. 92) of skill necessary to pass over steep icy sheep often running wild in the slopes. On one occasion two ewes Bavarian Alps ; but, on making survived the winter, but their lamb-. further inquiries at my request, he perished. 6 INHERITANCE. Chap. XIIL whether or not there has been any close degree of reversion. It is not known in any instance what variety was first turned out ; several varieties have probably in some cases run wild, and their crossing alone would tend to obliterate their proper character. Our domesticated animals and plants, when they run wild, must always be exposed to new conditions of life, for, as Mr. Wallace ll has well remarked, they have to obtain their own food, and are exposed to competition with the native productions. Under these circumstances, if our domesticated animals did not undergo change of some kind, the result would be quite opposed to the conclusions arrived at in this work. Nevertheless, I do not doubt that the simple fact of animals and plants becoming feral, does cause some tendency to reversion to the primitive state ; though this tendency has been much exaggerated by some authors. I will briefly run through the recorded cases. With neither horses nor cattle is the primitive stock known; and it has been shown in former chapters that they have assumed different colours in different countries. Thus the horses which have run wild in South America are generally brownish-bay, and in the East dun- coloured; their heads have become larger and coarser, and this may be due to reversion. No careful description has been given of the feral goat. Dogs which have run wild in various countries have hardly anywhere assumed a uniform character ; but they are probably descended from several domestic races, and aboriginally from several distinct species. Feral cats, both in Europe and La Plata, are regularly striped ; in some cases they have grown to an unusually large size, but do not differ from the domestic animal in any other character. When variously-coloured tame rabbits are turned out in Europe, they generally reacquire the colouring of the wild animal ; there can be no doubt that this does really occur, but we should remember that oddly-coloured and conspicuous animals would suffer much from beasts of prey and from being easily shot ; this at least was the opinion of a gentleman who tried to stock his woods with a nearly white variety ; if thus destroyed, they would be supplanted by, instead of being transformed into, the common rabbit. We have seen that the feral rabbits of Jamaica, and especially of Porto Santo, have assumed new colours and other new characters. The best known case of reversion, and that on which the widely spread belief in its universality apparently rests, is that of pigs. These animals have run wild in the West Indies, South America, and the Falkland Islands, and have everywhere II Pee some excellent remarks on Proc. Linn. Soc.,' 1858, vol. iii. p. 60 this subject by Mr. V'allace, 'Journal Chap. XIIl. REVERSION. 7 acquired the dark colour, the thick bristles, and great tusks of the -wild boar; and the young have reacquired longitudinal stripes. But even in the case of the pig, Roulin describes the half-wild animals in different parts of South America as differing in several respects. In Louisiana the pig12 has run wild, and is said to differ a little in form, and much in colour, from the domestic animal, yet does not closely resemble the wild boar of Europe. "With pigeons and fowls,13 it is not known what variety was first turned out, nor what character the feral birds have assumed. The guinea-fowl in the West Indies, when feral, seems to vary more than in the domesticated state. WTith respect to plants run wild, Dr. Hooker14 has strongly insisted on what slight evidence the common belief in their reversion to a primitive state rests. Godron15 describes wild turnips, carrots, and celery; but these plants in their cultivated state hardly differ from their wild prototypes, except in the succu- lency and enlargement of certain parts, — characters which would certainly be lost by plants growing in poor soil and struggling with other plants. No cultivated plant has run wild on so enormous a scale as the cardoon (Cynara cardunculus) in La Plata. Every botanist who has seen it growing there, in vast beds, as high as a horse's back, has been struck with its peculiar appearance ; but whether it differs in any important point from the cultivated Spanish form, which is said not to be prickly like its American descendant, or whether it differs from the wild Mediterranean species, which is said not to be social (though this may be due merely to the nature of the conditions), I do not know. Beversion to Characters derived from a Cross, in the case of Sub-varieties, Races, and Species. — When an individual having some recognisable peculiarity unites with another of the same sub-variety, not having the peculiarity in question, it often reappears in the descendants after an interval of several gene- rations. Every one must have noticed, or heard from old people of children closely resembling in appearance or mental disposition, or in so small and complex a character as expres- 12 Dureau de la Malle, in ' Comptes appear to me worth copying : but I now Rendus,' torn, xli., 1855, p. 807. find that Dureau de la Malle (' Comp- Frorathe statements above given, the tes Rendus,' torn, xli., 1855, p. 690) author roneludes that the wild pigs advances this as a good instance of of Louisiana are not descended from reversion to the primitive stock, and as the European Sus scrofa. confirmatory of a still more vague 13 Capt. W. Allen, in his ' Expe- statement in classical times by Varro. dit^on to the Niger,' states that fowls u ' Flora of Australia,' 1859, In- have run wild on the island of Anno- troduct., p. ix. bon, and have become modified in ls ' De l'Espece,' torn. ii. :f>. 54, form and voice. The account is so 58, 60. meagre and vague that it did not 8 INHERITANCE. Chap. XIII. sion, one of their grandparents, or some more distant collateral relation. Very many anomalies of structure and diseases,16 of which instances have been given in the last chapter, have come into a family from one parent, and have reappeared in the progeny after passing over two or three generations. The following case has been communicated to me on good authority, and may, I believe, be fully trusted : a pointer-bitch produced seven puppies ; four were marked with blue and white, which is so unusual a colour with pointers that she was thought to have played false with one of the greyhounds, and the whole litter was condemned ; but the gamekeeper was per- mitted to save one as a curiosity. Two years afterwards a friend of the owner saw the 3Toung dog, and declared that he was the image of his old pointer-bitch Sappho, the only blue and white pointer of pure descent which he had ever seen. This led to close inquiry, and it was proved that he was the great-great-grandson of Sappho ; so that, according to the common expression, he had only 1-1 6th of her blood in his veins. I may give one other instance, on the authority of Mr. E. Walker, a large cattle-breeder in Kincardineshire. He bought a black bull, the son of a black cow with white legs, white belly and part of the tail white; and in 1870 a calf the gr.-aT.-ffr.-srr.-STandcliild of this cow was born coloured in the same vei y peculiar manner ; all the inter- mediate offspring having been black. In these cases there can hardly be a doubt that a character derived from a cross with an individual of the same variety reappeared after passing over three generations in the one case, and five in the ■ other. When two distinct races are crossed, it is notorious that the tendency in the offspring to revert to one or both parent- forms is strong, and endures for many generations. I have myself seen the clearest evidence of this in crossed pigeons and with various plants. Mr. Sidney 1T states that, in a litter of Essex pigs, two young ones appeared which were the image of the Berkshire boar that had been used twenty-eight years ls Mr. Sedgwick gives many in- Julv, 18(33, pp. 448, 188. stances in the ' British and Foreign " In his edit, of ' Youatt on th& Med.-Chirurg. Review,' April and Pig,' 1860, p. 27. Chap. XIII. KEVEESION. 9 before in giving size and constitution to the breed. I ob- served in the farmyard at Betley Hall some fowls showing a strong likeness to the Malay breed, and was told by Mr. Toilet that he had forty years before crossed his birds with Malays ; and that, though he had at first attempted to get rid of this strain, he had subsequently given up the attempt in despair, as the Malay character would reappear. This strong tendency in crossed breeds to revert has given rise to endless discussions in how many generations after a single cross, either with a distinct breed or merely with an inferior animal, the breed may be considered as pure, and free from all danger of reversion. No one supposes that less than three generations sufiices, and most breeders think that six, seven, or eight are necessary, and some go to still greater lengths.13 But neither in the case of a breed which has been contaminated by a single cross, nor when, in the attempt to form an intermediate breed, half-bred animals have been matched together during many generations, can any rule be laid down how soon the tendency to reversion will be oblitera- ted. It depends on the difference in the strength or pre- potency of transmission in the two parent-forms, on their actual amount of difference, and on the nature of the con- ditions of life to which the crossed offspring are exposed. But we must be careful not to confound these cases of reversion to characters which were gained by a cross, with those under the first class, in which characters originally common to both parents, but lost at some former period, reappear ; for such characters may recur after an almost indefinite number of generations. The law of reversion is as powerful with hybrids, when they are sufficiently fertile to breed together, or when they are repeatedly crossed with either pure parent-form, as in the case of mongrels. It is not necessary to give instances. With plants almost every one who has worked on this sub- ject, from the time of Kolreuter to the present day, has insisted on this tendency. Gartner has recorded some good instances ; but no one has given more striking ones than 18 Dr. P. Lucas, ' Hered. Nat.,' ' Gard. Chronicle,' 1856, p. 620. 1 torn. ii. pp. 314, 892 : see a good could add a vast number of references, practical article on the subject in but they would be superfluous. 10 INHERITANCE. Chap. XIII. Kaudin.19 The tendency differs in degree or strength in different groups, and partly depends, as we -shall presently see, on whether the parent-plants have been long cultivated. Although the tendency to reversion is extremely general with nearly all mongrels and hybrids, it cannot be considered as invariably characteristic of them ; it may also be mastered by long-continued selection ; but these subjects will more properly be discussed in a future chapter on Crossing. From what we see of the power and scope of reversion, both in pure races, and when varieties or species are crossed, we may infer that characters of almost every kind are capable of reappear- ing after having been lost for a great length of time. But it does not follow from this that in each particular case certain characters will reappear ; for instance, this will not occur when a race is crossed with another endowed with prepotency of transmission. Sometimes the power of reversion wholly fails, without our being able to assign any cause for the failure : thus it has been stated that in a French family in which 85 out of above 600 members, during six generations, had been subject to night-blindness, " there has not been a single example of this affection in the children of parents who were themselves free from it."20 Reversion through Bud-propagation — Partial Reversion, by seg- ments in the same floiver or fruit, or in different parts of the body in the same individual animal. — In the eleventh chapter many cases of reversion by buds, independently of seminal genera- tion, were given — as when a leaf-bud on a variegated, a curled, or laciniated variety suddenly reassumes its proper character ; or as when a Provence-rose appears on a moss-rose, or a peach on a nectarine-tree. In some of these cases only half the flower or fruit, or a smaller segment, or mere stripes, reassume their former character ; and here we have reversion 19 Kolreuter gives curious cases in his ' Dritte Fortsetzung,' 1766, ss. 53, 59; and in his well-known 'Memoirs on Lavatera and Jalapa.' Gartner, ' Bastarderzeugung,' ss. 437, 441, &c. Naudin, in his " Recherches sur l'Hybridite," ' Nouvelles Archives du Museum,' torn. i. p. 25. 20 Quoted by Me. Sedgwick in ' Med.-Chirurg. Review,' April, 1861, p. 485. Dr. H. Dobell, in 'Med.- Chirurg. Transactions,' vol. xlvi., gives an analogous case, in which, in a large family, ringers with thickened joints were transmitted to several members during five generations ; but when the blemish once disappeared it never reappeared. Chap. XIII. REVERSION. 11 by segments. Yilmorin 21 lias also recorded several cases with plants derived from seed, of flowers reverting by stripes or blotches to their primitive colours : he states that in all such cases a white or pale-coloured variety must first be formed, and, when this is propagated for a length of time by seed, striped seedlings occasionally make their appearance ; and these can afterwards by care be multiplied by seed. The stripes and segments just referred to are not due, as far as is known, to reversion to characters derived from a cross, but to characters lost by variation. These cases, however, as Naudin22 insists in his discussion on disjunction of character, are closely analogous with those given in the eleventh chapter, in which crossed plants have been known to produce half- and-half or striped flowers and fruit, or distinct kinds of flowers on the same root resembling the two parent-forms. Many piebald animals probably come under this same head. Such cases, as we shall see in the chapter on Crossing, appa- rently result from certain characters not readily blending together, and, as a consequence of this incapacit}' for fusion, the offspring either perfectly resemble one of their two parents, or resemble one parent in one part, and the other parent in another part ; or whilst young are intermediate in character, but with advancing age revert wholly or by seg- ments to either parent-form, or to both. Thus, young trees of the Cytisus adami are intermediate in foliage and flowers between the two parent-forms ; but when older the buds continually revert either partially or wholly to both forms. The cases given in the eleventh chapter on the changes which occurred during growth in crossed plants of Tropseolum, Cereus, Datura, and Lathy rus are all analogous. As, however, these plants are hybrids of the first generation, and as their buds after a time come to resemble their parents and not their grandparents, these cases do not at first appear to come under the law of reversion in the ordinary sense of the word ; never- theless, as the change is effected through a succession of bud- generations on the same plant, they may be thus included. Analogous facts have been observed in the animal kingdom, 2 Verlot, ' Des Varietes,' 1865, torn. i. p. 25. Alex. Braun (in his ' Re- p. 63. juvenescenee,' RaySoc, 1853, p. 315* 22 'Nouvelles Archives du Mjseum,' apparently holds a similar opinion. 12 INHERITANCE. Chap. XIIL and are more remarkable, as they occur in the same individual in the strictest sense, and not as with plants through a suc- cession of bud-generations. With animals the act of rever- sion, if it can be so designated, does not pass over a true generation, but merely over the early stages of growth in the same individual. For instance, I crossed several white hens with a black cock, and many of the chickens were, during the first year, perfectly white, but acquired during the second year black feathers ; on the other hand, some of the chickens which were at first black, became during the second year piebald with white. A great breeder 23 says, that a Pencilled Brahma hen which has any of the blood of the Light Brahma in her, will " occasionally produce a pullet well pencilled during the first year, but she will most likely moult brown on the shoulders and become quite unlike her original colours in the second year." The same thing occurs with light Brahmas if of impure blood. I have observed exactly similar cases with the crossed offspring from differently coloured pigeons. But here is a more remarkable fact : I crossed a turbit, which has a frill formed by the feathers being reversed on its breast, with a trumpeter ; and one of the young pigeons thus raised at first showed not a trace of the frill, but, after moulting thrice, a small yet unmistakably distinct frill appeared on its breast. According to Girou,24 calves produced from a red cow by a black bull, or from a black cow by a red bull, are not rarely born red, and subsequently become black. I possess a dog, the daughter of a white terrier by a fox- coloured bulldog ; as a puppy she was quite white, but when about six months old a black spot appeared on her nose, and brown spots on her ears. \\ hen a little older she was badly wounded on the back, and the hair which grew on the cicatrix was of a brown colour, apparently derived from her father. This is the more remarkable, as with most animals having coloured hair, that which grows on a wounded surface is white. In the foregoing cases, the characters which with advancing age reappeared, were present in the immediately preceding 53 Mr. Teebay, in ' The Poultry "■* Quoted by Hofacker, ' Ueber die Book,' by Mr. Tegetmeier, 1866, p. Eigenschaften,' &c, s. 98. 73. Chap. XIII. REVERSION. 1 0 generations ; but characters sometimes reappear in the same manner after a much longer interval of time. Thus the calves of a hornless race of cattle which originated in Corrientes, though at first quite hornless, as they become adult sometimes acquire small, crooked, and loose horns ; and these in succeeding years occasionally become attached to the skull.25 White and black Bantams, both of which generally breed true, sometimes assume as they grow old a saffron or red plumage. For instance, a first-rate black bantam has been described, which during three seasons was perfectly black, but then annually became more and more red ; and it deserves notice that this tendency to change, whenever it occurs in a bantam, " is almost certain to prove hereditary."26 The cuckoo or blue-mottled Dorking cock, when old, is liable to acquire yellow or orange hackles in place of his proper bluish-grey hackles.27 Now as Gallus bankiva is coloured red and orange, and as Dorking fowls and bantams are descended from this species, we can hardly doubt that the change which occasionally occurs in the plumage of these birds as their age advances, results from a tendency in the individual to revert to the primitive type. Crossing as a direct cause of Reversion. — It has long been notorious that hybrids and mongrels often revert to both or to one of their parent-forms, after an interval of from two to seven or eight, or, according to some authorities, even a greater number of generations. But that the act of crossing in itself gives an impulse towards reversion, as shown by the reap- pearance of long-lost characters, has never, I believe, been hitherto proved. The proof lies in certain peculiarities, which do not characterise the immediate parents, and therefore can- not have been derived from them, frequently appearing in the offspring of two breeds when crossed, which peculiarities never appear, or appear with extreme rarity, in these same breeds, as long as they are precluded from crossing. As this 25 Azara, ' Essais Hist. Nat. de ' The Poultry Book,' by Mr. Teget. Paraguay,' torn. ii. 1801, p. 372. meier, 1866, p. 248. 26 These facts are given on the 27 'The Poultry Book,' by Teget- high authority of Mr. Hewitt, in meier, 1866, p. 97. 14 INHEEITANCE. Chap. XIII conclusion seems to me highly curious and novel, I will give the evidence in detail. My attention was first called to this subject, and I was led to make numerous experiments, by MM. Boitard and Corbie having stated that, when they crossed certain breeds of pigeons, birds coloured like the wild C. livia, or the common dovecot— namely, slaty-blue, with double black wing-bars, sometimes chequered with black, white loins, the tail barred with black, with the outer feathers edged with white,— were almost invariably produced. The breeds which I crossed, and the remarkable results attained, have been fully described in the sixth chapter. I selected pigeons belonging to true and ancient breeds, which had not a trace of blue or any of the above specified marks ; but when crossed, and their mongrels recrossed, young birds were often produced, more or less plainly coloured slaty-blue, with some or all of the proper charac- teristic marks. I may recall to the reader's memory one case, namely, that of a pigeon, hardly distinguishable from the wild Shetland species, the grandchild of a red-spot, white fantail, and two black barbs, from any of which, when purely-bred, the produc- tion of a pigeon coloured like the wild ft livia would have been almost a prodigy. I was thus led. to make the experiments, recorded in the seventh chapter, on fowls. I selected long-established pure breeds, in which there was not a trace of red, yet in several of the mongrels feathers of this colour appeared; and one magnificent bird, the offspring of a black Spanish cock and white Silk hen, was coloured almost exactly like the wild Gallus bankiva. All who know any- thing of the breeding of poultry will admit that tens of thousands of pure Spanish and of pure white Silk fowls might have been reared without the appearance of a red feather. The fact, given on the authority of Mr. Tegetmeier, of the frequent appearance, in mongrel fowls, of pencilled or transversely-barred feathers, like those common to many gallinaceous birds, is likewise apparently a case of reversion to a character formerly possessed by some ancient progenitor of the family. I owe to the kindness of this excellent observer the opportunity of inspecting some neck-hackles and tail- feathers from a hybrid between the common fowl and a very distinct species, the Oallus varius; and these feathers are transversely striped in a conspicuous manner with dark metallic blue and grey, a character which could not have been derived from either immediate parent. I have been informed by Mr. B. P. Brent, that he crossed a white Aylesbury drake and a black so-called Labrador duck, both of which are true breeds, and he obtained a young drake closely like the mallard {A. boschas). Of the musk-duck (A. moschata, Linn.) there are two sub-breeds, namely, white and slate-coloured ; and these I am informed breed true, or nearly true. Bat the Bev. W. D. Fox tells me that, by putting a white drake to a slate-coloured duck, Chap. XIIL REVERSION. 15 black birds, pied with white, like the wild musk-duck, were always produced. I hear from Mr. Blyth that hybrids from the canary and gold-finch almost always have streaked feathers on their backs ; and this streaking must be derived from the original wild canary. We have seen in the fourth chapter, that the so-called Himalayan rabbit, with its snow-white body, black ears, nose, tail, and feet, breeds perfectly true. This race is known to have been formed by the union of two varieties of silver-grey rabbits. Now, when a Himalayan doe was crossed by a sandy-coloured buck, a silver-grey rabbit was produced ; and this is evidently a case of reversion to one of the parent varieties. The young of the Himalayan rabbit are born snow-white, and the dark marks do not appear until some time subsequently ; but occasionally young Himalayan rabbits are born of a light silver-grey, which colour soon disappears ; so that here we have a trace of reversion, during an early period of life, to the parent varieties, independently of any recent cross. In the third chapter it was shown that at an ancient period some breeds of cattle in the wilder parts of Britain were white with dark ears, and that the cattle now kept half wild in certain parks, and those which have run quite wild in two distant parts of the world, are likewise thus coloured. Now, an experienced breeder, Mr. J. Beasley, of Northamptonshire,28 crossed some carefully selected West Highland cows with purely-bred shorthorn bulls. The bulls were red, red and white, or dark roan ; and the Highland cows were all of a red colour, inclining to a light or yellow shade. But a considerable number of the offspring— and Mr. Beasley calls attention to this as a remarkable fact— were white, or white with red ears. Bearing in mind that none of the parents were white, and that they were purely-bred animals, it is highly probable that here the offspring reverted, in consequence of the cross, to the colour of some ancient and half-wild parent-breed. The following case, perhaps, comes under the same head : cows in their natural state have their udders but little developed, and do not yield nearly so much milk as our domesticated animals. Now there is some reason to believe29 that cross-bred animals between two kinds, both of which are good milkers, such as Alderneys and Shorthorns, often turn out worthless in this respect. In the chapter on the Horse reasons were assigned for believing that the primitive stock was striped and dun-coloured ; and details were given, showing that in all parts of the world stripes of a dark colour frequently appear along the spine, across the legs, and on the shoulders, where they are occasionally double or treble, and even sometimes on the face and body of horses of all breeds and of all colours. But the stripes appear most frequently on the various :8 'Gardener's Chron. and Agri- of cattle as Mr. Willoughby Wood cultural Gazette,' 1866, p. 528. (' Gard. Chron.' 1869, p. 1216), admits -9 Ibid., 1860, p. 343. I am glad my principle of a cross giving a to find that so experienced a breeder tendency to reversion. 16 INHERITANCE. Chap. XIIL kinds of duns. In foals they are sometimes plainly seen, and subsequently disappear. The dun-colour and the stripes are strongly transmitted when a horse thus characterised is crossed with any other ; but I was not able to prove that striped duns are generally produced from the crossing of two distinct breeds, neither of which are duns, though this does sometimes occur. The legs of the ass are often striped, and this may considered as a reversion to the wild parent form, the Equus tseniopus of Abyssinia,30 which is generally thus striped. In the domestic animal the stripes on the shoulder are occasionally double, or forked at the extremity, as in certain zebrine species. There is reason to believe that the foal is more frequently striped on the legs than the adult animal. As with the horse, I have not acquired any distinct evidence that the crossing of differently-coloured varieties of the ass brings out the stripes. But now let us turn to the result of crossing the horse and ass. Although mules are not nearly so numerous in England as asses, I have seen a much greater number with striped legs, and with the stripes far more conspicuous than in either parent-form. Such mules are generally light-coloured, and might be called fallow- duns. The shoulder-stripe in one instance was deeply forked at the extremity, and in another instance was double, though united in the middle. Mr. Martin gives a figure of a Spanish mule with strong zebra-like marks on its legs,31 and remarks that mules are particu- larly liable to be thus striped on their legs. In South America, according to Koulin,32 such stripes are more frequent and con- spicuous in the mule than in the ass. In the United States, Mr. Gosse,33 speakinj; of these animals, says, " that in a great number, " perhaps in nine out of every ten, the legs are banded with " transverse dark stripes." Many years ago I saw in the Zoological Gardens a curious triple hybrid, from a bay mare, by a hybrid from a male ass and female zebra. This animal when old had hardly any stripes; but I was assured by the superintendent, that when young it had shoulder- stripes, and faint stripes on its flanks and legs. I mention this case more especially as an instance of the stripes being much plainer during youth than in old age. As the zebra has such a conspicuously striped body and legs, it might have been expected that the hybrids from this animal and the common ass would have had their legs in some degree striped ; but it appears from the figures given in D'r. Gray's 'Knowsley Gleanings,' and still more plainly from that given by Geoffroy and F. Cuvier,34 that the legs are much more conspicuously striped than the rest of the body ; and this fact is intelligible only on the belief 30 Sclater, in ' Proc. Zoolog. Soc.,' 1835, p. 338. 1882, p. 163. . 33 'Letters from Alabama,' 1859, p. 31 ' History of the Horse,' p. 212. 280. 32 ' Mem. presentes par divers 34 ' Hist. Nat. des Mammiferes, Savans a l'Acad. Royale,' torn. vi. 1820, torn. i. Chap. XIII. KE VERSION. 17 that the ass aids in giving, through the power of reversion, this character to its hybrid offspring. The quagga is banded over the whole front part of its body like a zebra, but has no stripes on its legs, or mere traces of them. But in the famous hybrid bred by Lord Morton,35 from a chestnut, nearly purely-bred, Arabian mare, by a male quagga, the stripes were " more strongly defined and darker than those on the legs of " the quagga." The mare was subsequently put to a black Arabian horse, and bore two colts, both of which, as formerly stated, were plainly striped on the legs, and one of them likewise had stripes on the neck and body. jLbe Equus indicus36 is characterised by a spinal stripe, without shoulder or leg stripes ; but traces of these latter stripes may occa- sionally be seen even hi the adult;37 and Colonel S. Poole, who has had ample opportunities for observation, informs me that in the foal, when first born, the head and legs are often striped, but the shoulder-stripe is not so distinct as in the domestic ass ; all these stripes, excepting that along the spine, soon disappear. Now a hybrid, raised at Knowsley38 from a female of this species by a male domestic ass, had all four legs transversely and conspicuously striped, had three short stripes on each shoulder and had even some zebra-like stripes on its face! Dr. Gray informs me that he has seen a second hybrid of the same parentage similarly striped. From these facts we see that the crossing of the several equine species tends in a marked manner to cause stripes to appear on various parts of the body, especially on the legs. As we do nut know whether the parent-form of the genus was striped, the appear- ance of the stripes can only hypothetically be attributed to reversion. But most persons, after considering the many undoubted cases of variously coloured marks reappearing by reversion in my experi- ments on crossed pigeons and fowls, will come to the same conclu- sion with respect to the horse-genus; and if so, we must admit that the progenitor of the group was striped on the legs, shoulders, lace, and probably over the whole body, like a zebra. Lastly, Professor Jaeger has given 39 a good case with pigs. He 35 ' Philosoph. Transact.,' 1821, p. these, as with the horse and ass. are 20. sometimes double: see Mr. Blyth. in 3S Solater, in ' Proc. Zoolog. Soc.,' the paper just quoted, and in ' Indian 1862, p. 163: this species is the Sporting Keview,' 1856, p. 3_'0 : and Ghor-Khur of N.W. India, and has Col. Hamilton Smith, in 'Nat. Library, often been called the Hemionus of Horses,' p. 318; and 'Diet. Class. Pallas. See, also, Mr. Myth's ex- d'Hist. Nat.,' torn. iii. p. 563. cellent paper in ' Journal of Asiatic 38 Figured in the ' Gleanings from Soc. of Bengal,' vol. xxviii., 1860, p. the Knowsley Menageries,' by Dr. J. 229. E. Gray. 37 Another species of wild ass, the 39 ' Darwin'sche Theorie und ilni true E. hemionus or Kiang, which Stellung zu Moral UDd Leligion,' p ordinarily has no shoulder-stripes, is 85. said occasionally to have them ; and VOL. II. C 18 INHERITANCE. Chai\ XIII. crossed the Japanese or masked breed with the common German breed, and the offspring were intermediate in character. He then re-crossed one of these mongrels with the pure Japanese, and in the litter thus produced one of the young resembled in all its characters a wild pig ; it had a long snout and upright ears, and was striped on the back. It should be borne in mind that the young of the Japanese breed are not striped, and that they have a short muzzle and ears remarkably dependent. A similar tendency to the recovery of long lost characters holds o-ood even with the instincts of crossed animals. There arc some breeds of fowls which are called " everlasting layers," because they have lost the instinct of incubation ; and so rare is it for them to incubate that I have seen notices published in works on poultry, when hens of such breeds have taken to sit.40 Yet the aboriginal species was of course a good incubator ; and with birds in a state of nature hardly any instinct is so strong as this. Now, so many cases have been recorded of the crossed offspring from two races, neither of which are incubators, becoming first-rate sitters, that the reappearance of this instinct must be attributed to reversion from crossing. One author goes so far as to say, " that a cross between two non- sitting varieties almost invariably produces a mongrel that becomes broody, and sits with remarkable steadiness." 41 Another author, after giving a striking ex- ample, remarks that the fact can be explained only on the principle that " two negatives make a positive." It cannot. however, be maintained that hens produced from a crosL 40 Cases of both Spanish and Polish from a cross between Golden and hens sitting are given in the ' Poultry Black Polish fowls, are "good and Chronicle,' 1855, vol. iii. p. 477. steady birds to sit." Mr. B. P. Brent 41 ' The Poultry Book,' by Mr. informs me that he raised some gooa Tegetmeier, 186(3, pp. 119, 163. The sitting hens by crossing Pencilled author, who remarks on the two Hamburg and Polish breeds. A negatives (' Journ. of Hort.,' 1862, cross-bred bird from a Spanish non- p. 325), states that two broods were incubating cock and Cochin incu- raised from a Spanish cock and Silver- batinghen is mentioned in the ' Poultry pencilled Hamburg hen, neither of Chronicle,' vol. iii. p. 13, as an "ex- which are incubators, and no less emplary mother." On the other than seven out of eight hens in these hand, an exceptional case is given m two broods "showed a perfect ob- the 'Cottage Gardener,' 1860, p. 388, stinacy in sitting." The Rev. E. S. of a hen raised from a Spanish cock Diron ('Ornamental Poultry,' 1848, and black Polish hen which did not p. 200) says that chickens reared incubate. Chap. XIII. EEVEESION. 19 between two non-sitting breeds invariably recover their lost instinct, any more than that crossed fowls or pigeons invari- ably recover the red or blue plumage of their prototypes. Thus I raised several chickens from a Polish hen by a Spanish cock, — breeds which do not incubate, — and none of the young hens at first showed any tendency to sit ; but one of them — the only one which was preserved — in the third year sat well on her eggs and reared a brood of chickens. So that here we have the reappearance with advancing age of a primitive instinct, in the same manner as we have seen that the red plumage of the Gallus banldva is sometimes reacquired both by crossed and purely-bred fowls of various kinds as they grow old. The parents of all our domesticated animals were of course aboriginally wild in disposition ; and when a domesticated species is crossed with a distinct species, whether this is a domesticated or only a tamed animal, the hybrids are often wild to such a degree, that the fact is intelligible only on the principle that the cross has caused a partial return to a primitive disposition. Thus, the Earl of Powis formerly im- ported some thoroughly domesticated humped cattle from India, and crossed them with English breeds, which belong to a distinct species ; and his agent remarked to me, without any question having been asked, how oddly wild the cross- bred animals were. The European wild boar and the Chinese domesticated pig are almost certainly specifically distinct : Sir F. Darwin crossed a sow of the latter breed with a wild Alpine boar which had become extremely tame, but the young, though having half-domesticated blood in their veins, were " extremely wild in confinement, and would not eat swill like common English pigs." Captain Hutton, in India, crossed a tame goat with a wild one from the Himalaya, and he re- marked to me how surprisingly wild the offspring were. Mr. Hewitt, who has had great experience in crossing tame cock-pheasants with fowls belonging to five breeds, gives as the character of all " extraordinary wildness ;"42 but I have myself seen one exception to this rule. Mr. S. J. Salter,4- 42 'The Poultry Book,' by Te?et- » ' Natnral Hietorj Bevmw," L863 ueier, 186(5, j>p. ltj.">, 107. April, p. 277. c 2 20 INHERITANCE. Chap. XIII. who raised a large number of hybrids from a bantam-hen by Gdllus sonneratii, states that "all were exceedingly wild." Mr. Waterton44 bred some wild ducks from eggs hatched under a common duck, and the young were allowed to cross freely both amongst themselves and with the tame ducks ; they were " half wild and half tame ; they came to the windows to be fed, but still they had a wariness about them quite remarkable." On the other hand, mules from the horse and ass are certainly not in the least wild, though notorious for obstinacy and vice. Mr. Brent, who has crossed canary-birds with many kinds of finches, has not observed, as he informs me, that the hybrids were in any way remarkably wild : but Mr. Jenner Weir who has had still greater experience, is of a directly opposite opinion. He remarks that the siskin is the tamest of finches, but its mules are as wild, when young, as newly caught birds, and are often lost through their continued efforts to escape. Hybrids are often raised between the common and musk duck, and I have been assured by three persons, who have kept these crossed birds, that they were not wild ; but Mr. Garnett45 observed that his hybrids were wild, and exhibited " migratory propensities " of which there is not a vestige in the common or musk duck. No case is known of this latter bird having escaped and become wild in Europe or Asia, except, according to Pallas, on the Caspian Sea ; and the common domestic cluck only occasionally becomes wild in districts where large lakes and fens abound. Never- theless, a large number of cases have been recorded46 of hj'brids from these two ducks having been shot in a com- pletely wild state, although so few are reared in comparison with purely-bred birds of either species. It is improbable that any of these hybrids could have acquired their wildness 44 'Essays on Natural History,' p. asserts ('Zoologist,' vol. v., 1845— 4b\ 917. p. 1:254) that several have been shot 45 As stated by Mr. Orton, in his in various parts of Belgium and ' Physiology of Breeding,' p. 12. Northern France. Audubon ('Ornith- 46 M. E. de Selys-Longehamps olog. Biography,' vol. iii. p. 168), refers ('Bulletin Acad. Roy. de Brux- speaking of these hybrids, says that, elles,' torn. xii. No. 10) to more than in North America, they " now and seven of these hybrids shot in then wander off and become quite Switzerland and France. JI. Debv wild." Chap. XIII. REVERSION. 21 from the musk-duck having paired with a truly wild duck ; and this is known not to be the case in North America ; hence we must infer that they have reacquired, through reversion, their wildness, as well as renewed powers of flight. These latter facts remind us of the statements, so frequently made by travellers in all parts of the world, on the degraded state and savage disposition of crossed races of man. That many excellent and kind-hearted mulattos have existed no one will dispute ; and a more mild and gentle set of men could hardly be found than the inhabitants of the island of Chilce, who consist of Indians commingled with Spaniards in various proportions. On the other hand, many years ago, long before I had thought of the present subject, I was struck with the fact that, in South America, men of complicated descent between Negroes, Indians, and Spaniards, seldom had, what- ever the cause might be, a good expression.47 Livingstone, — and a more unimpeachable authority cannot be quoted, — after speaking of a half-caste man on the Zambesi, described by the Portuguese as a rare monster of inhumanity, remarks, "It is unaccountable why half-castes, such as he, are so much more cruel than the Portuguese, but such is undoubtedly the case." An inhabitant remarked to Livingstone, " God made white men, and God made black men, but the Devil made half- castes." 4S "When two races, both low in the scale, are crossed the progeny seems to be eminently bad. Thus the noble- hearted Humboldt, who felt no prejudice against the inferior races, speaks in strong terms of the bad and savage disposition of Zambos, or half-castes between Indians and Negroes : and this conclusion has been arrived at by various observers.49 From these facts we may perhaps infer that the degraded state of so many half-castes is in part due to reversion to a primitive and savage condition, induced by the act of crossing, even if mainly due to the unfavourable moral conditions under which they are generally reared. Summary on the proximate causes leading to Reversion. — "When 47 'Journal of Researches,' 1843, 49 Dr. P. Broca, on 'Hybridity in. p. 71. the Genus Homo,' Eng. translat. 48 'Expedition to the Zambesi,' 1864, p. 39. 1865, pp. 25, 150. 22 INHERITANCE. Chap. XIII. purely-bred animals or plants reassume long-lost characters, — when the common ass, for instance, is born with striped legs, when a pure race of black or white pigeons throws a slaty- blue bird, or when a cultivated heartsease with large and rounded flowers produces a seedling with small and elongated flowers, — we are quite unable to assign any proximate cause. When animals run wild, the tendency to reversion, which, though it has been greatly exaggerated, no doubt exists, is sometimes to a certain extent intelligible. Thus, with feral pigs, exposure to the weather will probably favour the growth of the bristles, as is known to be the case with the hair of oTher domesticated animals, and through correlation the tusks will tend to be redeveloped. But the reappeaiance of coloured longitudinal stripes on young feral pigs cannot be attributed to the direct action of external conditions. In this case, and in many otheis, we can only say that any change in the habits of life apparently favour a tendency, inherent or latent in the species, to return to the primitive state. It will be shown in a future chapter that the position of flowers on the summit of the axis, and the position of seeds within the capsule, sometimes determine a tendency towards reversion ; and this apparently depends on the amount of sap or nutriment which the flower-buds and seeds receive. The position, also, of buds, either on branches or on roots, some- times determines, as was formerly shown, the transmission of the character proper to the variety, or its reversion to a former state. "We have seen in the last section that when two races or species are crossed there is the strongest tendency to the re- appearance in the offspring of long-lost characters, possessed by neither parent nor immediate progenitor. When two white, or red, or black pigeons, of well-established breeds, are united, the offspring are almost sure to inherit the same colours ; but when differently- coloured birds are crossed, the opposed forces of inheritance apparently counteract each other, and the tendency which is inherent in both parents to produce slaty-blue offspring becomes predominant. So it is in several other cases. But when, for instance, the ass is crossed with E. indicus or with the horse, — animals which Chap. XIII. REVERSION. 23 have not striped legs,— and the hybrids have conspicuous stripes on their legs and even on their faces, all that can be said is, that an inherent tendency to reversion is evolved through some disturbance iu the organisation caused by the act of crossing. Another form of reversion is far commoner, indeed is almost universal with the offspring from a cross, namely, to the characters proper to either pure parent-form. As a geneial rule, crossed offspring in the first generation are nearly inter- mediate between their parents, but the grandchildren and succeeding generations continually revert, in a greater or lesser degree, to one or both of their progenitors. Several authors have maintained that hybrids and mongrels include all the characters of both parents, not fused together, but merely mingled in different proportions in different parts of the body ; or, as Kaudin 50 has expressed it, a hybrid is a living mosaic-work, in which the eye cannot distinguish the discordant elements, so completely are they intermingled. "We can hardly doubt that, in a certain sense, this is true, as when we behold in a hybrid the elements of both species seo-reo-ating- themselves into segments in the same flower or fruit, by a process of self-attraction or self-affinity ; this segregation taking place either by seminal or bud-propagation. Naudin further believes that the segregation of the two specific elements or essences is eminently liable to occur in the male and female reproductive matter ; and he thus explains the almost universal tendency to reversion in succes- sive hybrid generations. For this would be the natural result of the union of pollen and ovules, in both of which the elements of the same species had been segregated by self- affinity. If, on the other hand, pollen which included the elements of one species happened to unite with ovules includ- ing the elements of the other species, the intermediate or hybrid state would still be retained, and there would be no reversion. But it would, as I suspect, be more correct to say that the elements of both parent-species exist in every hybrid in a double state, namely, blended together and com- 50 'Nouvclles Archives du Museum,' torn. i. p. 151. 24 INHERITANCE. Chap. XIII. pletely separate. How this is possible, and what tl 3 term specific essence or element may be supposed to express, I shall attempt to show in the chapter on the hypothesis of pangenesis. But Naudin's view, as propounded by him, is not applicable to the reappearance of characters lost long ago by variation ; and it is hardly applicable to races or species which, after having been crossed at some former period with a distinct form, and having since lost all traces of the cross, neverthe- less occasionally yield an individual which reverts (as in the case of the great-great-grandchild of the pointer Sappho) to the crossing form. The most simple case of reversion, namely, of a hybrid or mongrel to its grandparents, is connected by an almost perfect series with the extreme case of a purely-bred race recovering characters which had been lost during many ages ; and we are thus led to infer that all the cases must be related by some common bond. Gartner believed that only highly sterile hybrid plants ex- hibit any tendency to reversion to their parent-forms. This erroneous belief may perhaps be accounted for by the nature of the .genera crossed by him, for he admits that the tendency differs in different genera. The statement is also directly con- tradicted by Naudin's observations, and by the notorious fact that perfectly fertile mongrels exhibit the tendency in a high degree, — even in a higher degree, according to Gartner himself, than hybrids.51 Gartner further states that reversions rarely occur with hybrid plants raised from species which have not been culti- vated, whilst, with those which have been long cultivated, they are of frequent occurrence. This conclusion explains a curious discrepancy : Max Wichura,52 who worked exclu- sively on willows which had not been subjected to culture, never saw an instance of reversion ; and he goes so far as to suspect that the careful Gartner had not sufficiently protected his hybrids from the pollen of the parent-species : Naudin, on the other hand, who chiefly experimented on cucurbitaceous and other cultivated plants, insists more strenuously than any other 51 ' Bastarderzeugung,' s. 582, 438, der Weiden,' 1865, s. 23. For Gartner's &c. remarks on this head, see ' Bastard- 52 ' Die Bastardbefruchtuug .... erzeugung,' s. 474, 582. Chap. XIII. REVERSION. 25 author on the tendency to reversion in all hybrids. The con- clusion that the condition of the parent-species, as affected by culture, is one of the proximate causes leading to reversion, agrees well with the converse case of domesticated animals and cultivated plants being liable to reversion when they become feral ; for in both cases the organisation or constitution must be disturbed, though in a very different way.53 Finally, we have seen that characters often reappear in purely-bred races without our being able to a>-sign any proximate cause ; but when they become feral this is either indirectly or directly induced by the change in their condi- tions of life. With crossed breeds, the act of crossing in itself certainly leads to the recovery of long-lost characters, as well as of those derived from either parent-form. Changed conditions, consequent on cultivation, and the relative position of buds, flowers, and seeds on the plant, all apparently aid in giving this same tendency. Keversion may occur either through seminal or bud generation, generally at birth, but sometimes only with an advance of age. Segments or portions of the individual may alone be thus affected. That a being should be born resembling in certain characters an ancestor removed by two or three, and in some cases by hundreds or even thousands of generations, is assuredly a wonderful fact. In these cases the child is commonly said to inherit such characters directly from its grandparent, or more remote ancestors. But this view is hardly conceivable. If, however, we suppose that every character is derived exclusively from the father or mother, but that many characters lie latent or dormant in both parents during a long succession of genera- tions, the foregoing facts are intelligible. In what manner characters may be conceived to lie latent, will be considered in a future chapter to which I have lately alluded. Latent Characters. — But I must explain what is meant by 53 Prof. Weismann, in his very elusion, namely, that any cause which curious essay on the different forms disturbs the organisation, such as the produced by the same species of exposure of the cocoons to heat ox butterfly at different seasons (' Saison- even to much shaking, gives a Dimorphismus der Schmetterlinge,' pp. tendency to reversion. 27, 28), has come to a similar con- 2G INHERITANCE. Chap. XIII. characters lying latent. The most obvious illustration is afforded by secondary sexual characters. In every female all the secondary male characters, and in every male all the secondary female characters, apparently exist in a latent state, ready to be evolved under certain conditions. It is well known that a large number of female birds, such as fowls, various pheasants, partridges, peahens, ducks, &c., when old or diseased, or when operated on, assume many or all of the secondary male characters of their species. In the case of the hen-pheasant this has been observed to occur far more frequently during certain years than during others.54 A duck ten years old has been known to assume both the perfect winter and summer plumage of the drake.55 "Water- ton 56 gives a curious case of a hen which had ceased laying, and had assumed the plumage, voice, spurs, and warlike disposition of the cock ; when opposed to an enemy she would erect her hackles and show fight. Thus every character, even to the instinct and manner of fighting, must have lain dormant in this hen as long as her ovaria continued to act. The females of two kinds of deer, when old, have been known to acquire horns ; and, as Hunter has remarked, we see some- thing of an analogous nature in the human species. On the other hand, with male animals, it is notorious that the secondary sexual characters are more or less completely lost when they are subjected to castration. Thus, if the operation be performed on a young cock, he never, as Yarrell states, crows again ; the comb, wattles, and spurs do not grow to their full size, and the hackles assume an intermediate appearance between true hackles and the feathers of the hen. Cases are recorded of confinement, which often affects the reproductive system, causing analogous results. But cha- 54 Yarrell, 'Phil. Transact.,' 1827, Isidore Geoffroy Saint-Hilaire, in his p. 268 ; Dr. Hamilton, in ' Proc. ' Essais de Zoolog. Gen.' (' suites a Zoolog. Soc.,' 1862, p. 23. Buffon,' 184-2, pp. 496-513), has 55 ' Archiv. Skand. Beitrage zur collected such cases in ten different Naturgesch.' viii. s. 397-413. kinds of birds. It appears that 56 In his ' Essays on Nat. Hist.,' Aristotle was well aware of the 1838, Mr. Hewitt gives analogous change in mental disposition in old cases with hen-pheasants in ' Journal hens. The case of the female deer of Horticulture, July 12, 1864, p. 37. acquiring horns is given at p. 513. Chap. XIII. KE VERSION. 27 racters properly confined to the female are likewise acquired by the male ; the capon takes to sitting on eggs, and will bring up chickens ; and what is more curious, the utterly sterile male hybrids from the pheasant and the fowl act in the same manner, " their delight being to watch when the hens leave their nests, and to take on themselves the office of a sitter." 57 That admirable observer Reaumur 58 asserts that a cock, by being long confined in solitude and darkness, can be taught to take charge of young chickens ; he then utters a peculiar cry, and retains during his whole life this newly acquired maternal instinct. The many well-ascertained cases of various male mammals giving milk shows that their rudi- mentary mammary glands retain this capacity in a latent condition. We thus see that in many, probably in all cases, the secondary characters of each sex lie dormant or latent in the opposite sex, ready to be evolved under peculiar circumstances. \\ e can thus understand how, for instance, it is possible for a o-ood milking cow to transmit her good qualities through her male offspring to future generations ; for we may confi- dently believe that these qualities are present, though latent, in the males of each generation. So it is with the game-cock, who can transmit his superiority in courage and vigour through his female to his male offspring ; and with man it is known 59 that diseases, such as hydrocele, necessarily confined to the male sex, can be transmitted through the female to the grandson. Such cases as these offer, as was remarked at the commencement of this chapter, the simplest possible examples of reversion ; and they are intelligible on the belief that characters common to the grandparent and grandchild of the same sex are present, though latent, in the intermediate parent of the opposite sex. The subject of latent characters is so important, as we shall see in a future chapter, that I will give another illustration. Many animals have the right and left sides of their body 57 ' Cottage Gardener,' 1860, p. 50 Sir H. Holland, ' Medical Notes 379. and Reflections,' 3rd edit., 1855, p. 38 ' Art de faire Eclorc,' &c, 1749, 31. torn. ii. p. 8. 28 INHERITANCE. Chap. XIII. unequally developed : this is well known to be the case with flat-fish, in which the one side differs in thickness and colour and in the shape of the fins, from the other, and during the growth of the young fish one eye is gradually twisted from the lower to the upper surface.60 In most flat-fishes the left is the blind side, but in some it is the right ; though in both cases reversed or" wrong fishes," are occasionally developed ; and in Platessa flcsus the right or left side is indifferently the upper one. With gasteropods or shell-fish, the right and left sides are extremely unlike ; the far greater number of species are dextral, with rare and occasional reversals of development, and some few are normally sinistral ; but certain sjaecies of Bulimus, and many Achatinella?,61 are as often sinistral as dextral. I will give an analogous case in the great articulate kingdom : the two sides of Verruca62 are so wonderfully unlike, that without careful dissection it is extremely difficult to recognise the corresponding parts on the opposite sides of the body ; yet it is apparently a mere matter of chance whether it be the right or the left side that undergoes so singular amount of change. One plant is known to me 63 in which the flower, according as it stands on the one or other side of the spike, is unequally developed. In all the foregoing cases the two sides are perfectly symmetrical at an early period of growth. Now, whenever a species is as liable to be unequally developed on the one as on the other side, we may infer that the capacity for such development is present, though latent, in the undeveloped side. And as a reversal of development occasionally occurs in animals of many kinds, this latent capacity is probably very common. The best yet simplest cases of characters lying dormant are, perhaps, those previously given, in which chickens and young pigeons, raised from a cross between differently coloured 60 See Steenstrup on the ' Obliquity p. 209. of Flounders' : in ' Annals and Mag. of 62 Darwin, ' Balanitis?,' Ray Soc, Nat. Hist.' May, 1865, p. 361. I 1854, p. 499 : see also the appended have given an abstract of Malm's remarks on the apparently capricious explanation of this wonderful pheno- development of the thoracic limbs on menon in the ' Origin of Species' 6th the right and left sides in the higher Edit. p. 186. crustaceans. 61 Dr. E. von Martens, in ' Annals ei Mormodes ignea : Darwin, ' Fer- nnd Mag. of Nat. Hist.' March, 1866, tilisation of Orchids,' 1862, p. 251. Chap. XIII. REVERSION. 29 birds, are at first of one colour, but in a year or two acquire feathers of the colour of the other parent ; for in this case the tendency to a change of plumage is clearly latent in the young bird. So it is with hornless breeds of cattle, some of which acquire small horns as they grow old. Purely bred black and white bantams, and some other fowls, occasionally assume, with advancing years, the red feathers of the parent-species. I will here add a somewhat different case, as it connects in a striking manner latent characters of two classes. Mr. Hewitt G4 pos- sessed an excellent Sebright gold-laced bantam hen, which, as she became old, grew diseased in her ovaria, and assumed male characters. In this breed the males resemble the females in all respects except in their combs, wattles, spurs, and instincts ; hence it might have been expected that the diseased hen would have assumed only those masculine characters which are proper to the breed, but she acquired, in addition, well-arched tail sickle-feathers quite a foot in length, saddle- feathers on the loins, and hackles on the neck, — ornaments which, as Mr. Hewitt remarks, " would be held as abominable in this breed." The Sebright bantam is known 65 to have originated about the year 1800 from a cross between a common bantam and a Polish fowl, recrossed by a hen-tailed bantam, and carefully selected ; hence there can hardly be a doubt that the sickle-feathers and hackles which appeared in the old hen were derived from the Polish fowl or common bantam ; and we thus see that not only certain masculine characters proper to the Sebright bantam, but other masculine characters derived from the first progenitors of the breed, removed by a period of above sixty years, were lying latent in this henbird, ready to be evolved as soon as her ovaria became diseased. From these several facts it must be admitted that certain characters, capacities, and instincts, may lie latent in an indi- vidual, and even in a succession of individuals, without our being able to detect the least sign of their presence. When fowls, pigeons, or cattle of different colours are crossed, and 64 ' Journal of Horticulture,' July, Tegetmeier. 1864, p. 33. I have had the oppor- 8S ' The Poultry Book,' by Mr tunity of examining these remarkable Tegetmeier, 1866, p. 241. feathers through the kindness of Mr 8() INHERITANCE. Chap. XIII. their offspring change colour as they grow old, or when the crossed turbit acquired the characteristic frill after its third moult, or when purely-bred bantams partially assume the red plumage of their prototype, we cannot doubt that these qualities were from the first present, though latent, in the individual animal, like the characters of a moth in the cater- pillar. Now, if these animals had produced offspring before they had acquired with advancing age their new characters, nothing is more probable than that they would have trans- mitted them to some of their offspring, who in this case would in appearance have received such characters from their grand- parents or more distant progenitors. AYe should then have had a case of reversion, that is, of the reappearance in the child of an ancestral character, actually present, though during youth completely latent, in the parent ; and this we may safely conclude is what occurs in all reversions to pro- genitors, however remote. This view of the latency in each generation of all the cha- racters which appear through reversion, is also supported by their actual presence in some cases during early youth alone, or by their more frequent appearance and greater distinctness at this age than during maturity. We have seen that this is often the case with the stripes on the legs and faces of the several species of the horse-genus. The Himalayan rabbit, when crossed, sometimes produces offspring which revert to the parent silver-grey breed, and we have seen that in purely bred animals pale-grey fur occasionally reappears during early youth. Black cats, we may feel assured, would occasionally produce by reversion tabbies ; and on young black kittens, with a pedigree66 known to have been long pure, faint traces of stripes may almost always be seen which afterwards dis- appear. Hornless Suffolk cattle occasionally produce by reversion horned animals ; and Youatt 67 asserts that even in hornless individuals " the rudiment of a horn may be often felt at an early age." No doubt it appears at first sight in the highest degree im- probable that in every horse of every generation there should 6G Carl Vogt, ' Lectures on Man,' 67 ' Cb Cattle,' p. 174. Eag. translat., 1864, p. 411. Chap. XIII. EEVERSIOX. 81 be a latent capacity and tendency to produce stripes, though these may not appear once in a thousand generations ; that in every white, black, or other coloured pigeon, which may have transmitted its proper colour during centuries, there should be a latent capacity in the plumage to become blue and to be marked with certain characteristic bars ; that in every child in a six-fingered family there should be the capacity for the production of an additional digit ; and so in other cases. Nevertheless, there is no more inherent improbability in this being the case than in a useless and rudimentary organ, or even in only a tendency to the production of a rudimentary organ, being inherited during millions of generations, as- is well known to occur with a multitude of organic beings. There is no more inherent improbability in each domestic pig, during a thousand generations, retaining the capacity and tendency to develop great tusks under fitting conditions, than in the young calf having retained for an indefinite number of generations rudimentary incisor teeth, which never protrude through the gums. I shall give at the end of the next chapter a summary of the three preceding chapters ; but as isolated and striking cases of reversion have here been chiefly insisted on, I wish to guard the reader against supposing that reversion is due to some rare or accidental combination of circumstances. When a character, lost during hundreds of generations, suddenly reappears, no doubt some such combination must occur ; but reversions to the immediately preceding generations may be constantly observed, at least, in the offspring of most unions. This has been universally recognised in the case of hybrids and mongrels, but it has been recognised simply from the difference between the united forms rendering the resemblance of the offspring to their grandparents or more remote pro- genitors of easy detection. Eeversion is likewise almost in- variably the rule, as Mr. Sedgwick has shown, with certain diseases. Hence we must conclude that a tendency to this peculiar form of transmission is an integral part of the general law of inheritance. Monstrosities. — A large number of monstrous growths and 32 INHERITANCE. Chap. XIII. of lesser anomalies are admitted by every one to be due to an arrest of development, that is, to the persistence of an embry- onic condition. But many monstrosities cannot be thus explained ; for parts of which no trace can be detected in the embryo, but which occur in other members of the same class of animals occasionally appear, and these may probably with truth be attributed to reversion. As, however, I have treated this subject as fully as I could in my ' Descent of Man ' (chap, i., 2nd edit.), I will not here recur to it. When flowers which have normally an irregular structure become regular or peloric, the change is generally looked at by botanists as a return to the primitive state. But Dr. Maxwell Masters, 6S who has ably discussed this subject, remarks that when, for instance, all the sepals of a Tropseolum become green and of the same shape, instead of being coloured with one prolonged into a spur, or when all the petals of a Linaria become simple and regular, such cases may be due merely to an arrest of development ; for in these flowers all the organs during their earliest condition are symmetrical, and, if arrested at this stage of growth, they would not become irregular. If, moreover, the arrest were to take place at a still earlier period of development, the result would be a simple tuft of green leaves ; and no one probably would call this a case of* reversion. Dr. Masters designates the cases first alluded to as regular peloria ; and others, in which all the corresponding parts assume a similar form of irregularity, as when all the petals in a Linaria become spurred, as irregular peloria. We have no right to attribute these latter cases to reversion, until it can be shown that the parent-form, for instance, of the genus Linaria had had all its petals spurred ; for a chance of this nature might result from the spreading of an anomalous structure, in accordance with the law, to be discussed in a future chapter, of homologous parts tending to vary in the same manner. But as both forms of peloria frequently occur on the same individual plant of the Linaria,69 they probably stand in some close relation to one another. On the doctrine that peloria is simply the result of an arrest of development, it is difficult to understand how an organ arrested at a very early period of growth should acquire its full functional perfection ; — how a petal, supposed to be thus arrested, should acquire its brilliant colours, and serve as an envelope to the flower, or a stamen produce efficient pollen ; yet this occurs with 68 ' Natural Hist. Review,' April, cases, Sitzb. d. k. Akad. d. Wissensch. : 1863, p. 258. See also his Lecture, Wien. B 1. LX. and especially Bd. Royal Institution, March 16, 1860. LXVI., 1872, p. 125. On same subject, see Moquin-Tandon, 69 Verlot, ' Des Varietes,' 1865, p. ' Elements de Teratologic,' 1841, pp. 89; Naudin, 'Nouvelles Archives du 184,352 Dr. Peyritsch has collected Museum.' torn. i. p 117. a large number of very interesting CiUP. XIII. REVERSION. 33 many peloric flowers. That pelorism is not due to mere chance variability, but either to an arrest of development or to reversion, we may infer from an observation made by Ch. Morren,7u namely, that families which have irregular flowers often " return by these monstrous growths to their regular form; whilst we never see a regular flower realise the structure of an irregular one." Some flowers have almost certainly become more or less completely peloric through reversion, as the following interesting case shows. Corydalis tuberosa properly has one of its two nectaries colourless, destitute of nectar, only half the size of the other, and therefore, to a certain extent, in a rudimentary state; the pistil is curved towards the perfect nectary, and the hood, formed of the inner IDetals, slips off the pistil and stamen in one direction alone, so that, when a bee sucks the perfect nectary, the stigma and stamens are exposed and rubbed against the insect's body. In several closely allied genera, as in Dielytra, &c, there are two perfect nectaries, the pistil is straight, and the hood slips off on either side, accord- ing as the bee sucks either nectary. Now, I have examined several flowers of Corydalis tuberosa, in which both nectaries were equally developed and contained nectar ; in this we see only the redevelop- ment of a partially aborted organ ; but with this redevelopment the pistil becomes straight, and the hood slips off in either direction , so that these flowers have acquired the perfect structure, so well adapted for insect agency, of Dielytra and its allies. We cannot attribute these coadapted modifications to chance, or to correlated variability; we must attribute them to reversion to a primordial condition of the species. The peloric flowers of Pelargonium have their five petals in all respects alike, and there is no nectary ; so that they resemble the symmetrical flowevs of the closely allied genus Geranium ; but the alternate stamens are also sometimes destitute of anthers, the shortened filaments being left as rudiments, and in this respect they resemble the symmetrical flowers of the closely allied genus Erodium. Hence we may look at the peloric flowers of Pelargo- nium as haviug reverted to the state of some primordial form, the progenitor of the three closely related genera of Pelargonium, Geranium, and Erodium. In the peloric form of Antirrhinum majus, appropriately called the " Wonder," the tubular and elongated flowers differ wonderfully from those of the common snapdragon ; the calyx and the mouth of the corolla consist of six equal lobes, and include six equal instead of four unequal stamens. One of the two additional stamens is manifestly formed by the development of a microscopically minute papilla, which may be found at the base of the upper lip of the flower of the common snapdragons in the nineteen plants examined 70 In his discussion on some curious nal of Horticulture,' Feb. 24, 18G3j peloric Calceolarias, yjoted in 'Jour- p. 152. VOL. II 4 INHERITANCE. Chap. XIII. by ine. That this papilla is a rudiment of a stamen was well shown 1 >y its various degrees of development in crossed plants between the common and the peloric Antirrhinum. Again, a peloric Galeob-