The Variation of Animals and Plants under Domestication Volume I Part 21

There are seven dorsal vertebrae bearing ribs; the first dorsal is never anchylosed with the succeeding four, which are generally anchylosed together. In one Sultan fowl, however, the two first dorsal vertebrae were free. In two skeletons, the fifth dorsal was free; generally the sixth is free (as in G. bankiva), but sometimes only at its posterior end, where in contact with the seventh. The seventh dorsal vertebra, in every case excepting in one Spanish c.o.c.k, was anchylosed with the lumbar vertebrae. So that the degree to which these middle dorsal vertebrae are anchylosed is variable.

Seven is the normal number of true ribs, but in two skeletons of the Sultan fowl (in which the fourteenth cervical vertebra was not furnished with little ribs) there were eight pairs; the eighth pair seemed to be developed on a vertebra corresponding with the first lumbar in G. bankiva; the sternal portion of both the seventh and eighth ribs did not reach the sternum. In four skeletons in which ribs were developed on the fourteenth cervical vertebra, there were, when these cervical ribs are included, eight pairs; but in one Game c.o.c.k, in which the fourteenth cervical was furnished with ribs, there were only six pairs of true dorsal ribs; the sixth pair in this case did not have processes, and thus resembled the seventh pair in other skeletons; in this Game c.o.c.k, as far as could be judged from the appearance of the lumbar vertebrae, a whole dorsal vertebra with its ribs was missing. We thus see that the ribs (whether or not the little pair attached to the fourteenth cervical vertebra be counted) vary from six to eight pair. The sixth pair is frequently not furnished with processes. The sternal portion of the seventh pair is extremely broad in Cochins, and is completely ossified. As previously stated, it is scarcely possible to count the lumbo-sacral vertebrae; but they certainly do not correspond in shape or number in the several skeletons. The caudal vertebrae are closely similar in all the skeletons, the only difference being whether or not the basal one is anchylosed to the pelvis; they hardly vary even in length, not being shorter in Cochins, with their short tail-feathers, than in other breeds; in a Spanish c.o.c.k, however, the caudal vertebrae were a little elongated. In three rumpless fowls the caudal vertebrae were few in number, and anchylosed together into a misformed ma.s.s.

In the individual vertebrae the differences in structure are very slight.

In the atlas the cavity for the occipital condyle is either ossified into a ring, or is, as in Bankiva, open on its upper margin. The upper arc of the spinal ca.n.a.l is a little more arched in Cochins, in conformity with the shape of the occipital foramen, than in G. bankiva. In several skeletons a difference, but not of much importance, may be observed, which commences at the fourth cervical vertebra, and is greatest at about the sixth, seventh, or eighth vertebra; this consists in the haemal descending processes being united to the body of the vertebra by a sort of b.u.t.tress.

This structure may be observed in Cochins, Polish, some Hamburghs, and probably other breeds; but is absent, or barely developed, in Game, Dorking, Spanish, Bantam, and several other breeds examined by me. On the dorsal surface of the sixth cervical vertebra in Cochins three prominent points are more strongly developed than in the corresponding vertebra of the Game fowl or G. bankiva.

PELVIS.

This differs in some few points in the several skeletons. The anterior margin of the ilium seems at first to vary much in outline, but this is chiefly due to the degree to which the margin in the middle part is ossified to the crest of the vertebrae; the outline, however, does differ in being more truncated in Bantams, and more rounded in certain breeds, as in Cochins. The outline of the ischiadic foramen differs considerably, being nearly circular in Bantams, instead of egg-shaped as in the Bankiva, and more regularly oval in some skeletons, as in the Spanish. The obturator notch is also much less elongated in some skeletons than in others. The end of the pubic bone presents the greatest difference; being hardly enlarged in the Bankiva; considerably and gradually enlarged in Cochins, and in a lesser degree in some other breeds; and abruptly enlarged in Bantams. In one Bantam this bone extended very little beyond the extremity of the ischium. The whole pelvis in this latter bird differed widely in its proportions, being far broader proportionally to its length than in Bankiva.

(FIGURE 38. EXTREMITY OF THE FURCULA, of natural size, viewed laterally. A.

Wild Gallus bankiva. B. Spangled Polish Fowl. C. Spanish Fowl. D. Dorking Fowl.)

STERNUM.

This bone is generally so much deformed that it is scarcely possible to compare its shape strictly in the several breeds. The form of the triangular extremity of the lateral processes differs considerably, being either almost equilateral or much elongated. The front margin of the crest is more or less perpendicular and varies greatly, as does the curvature of the posterior end, and the flatness of the lower surface. The outline of the manubrial process also varies, being wedge-shaped in the Bankiva, and rounded in the Spanish breed. The FURCULUM differs in being more or less arched, and greatly, as may be seen in the accompanying outlines, in the shape of the terminal plate; but the shape of this part differed a little in two skeletons of the wild Bankiva. The CORACOID presents no difference worth notice. The SCAPULA varies in shape, being of nearly uniform breadth in Bankiva, much broader in the middle in the Polish fowl, and abruptly narrowed towards the apex in the two Sultan fowls.

I carefully compared each separate bone of the leg and wing, relatively to the same bones in the wild Bankiva, in the following breeds, which I thought were the most likely to differ; namely, in Cochin, Dorking, Spanish, Polish, Burmese Bantam, Frizzled Indian, and black-boned Silk fowls; and it was truly surprising to see how absolutely every process, articulation, and pore agreed, though the bones differed greatly in size.

The agreement is far more absolute than in other parts of the skeleton. In stating this, I do not refer to the relative thickness and length of the several bones; for the tarsi varied considerably in both these respects.

But the other limb-bones varied little even in relative length.]

Finally, I have not examined a sufficient number of skeletons to say whether any of the foregoing differences, except in the skull, are characteristic of the several breeds. Apparently some differences are more common in certain breeds than in others,--as an additional rib to the fourteenth cervical vertebra in Hamburghs and Games, and the breadth of the end of the pubic bone in Cochins. Both skeletons of the Sultan fowl had eight dorsal vertebrae, and the end of the scapula in both was somewhat attenuated. In the skull, the deep medial furrow in the frontal bones and the vertically elongated occipital foramen seem to be characteristic of Cochins; as is the great breadth of the frontal bones in Dorkings; the separation and open s.p.a.ces between the tips of the ascending branches of the premaxillaries and nasal bones, as well as the front part of the skull being but little depressed, characterise Hamburghs; the globular shape of the posterior part of the skull seems to be characteristic of laced Bantams; and lastly, the protuberance of the skull with the ascending branches of the premaxillaries partially aborted, together with the other differences before specified, are eminently characteristic of Polish and other Crested fowls.

But the most striking result of my examination of the skeleton is the great variability of all the bones except those of the extremities. To a certain extent we can understand why the skeleton fluctuates so much in structure; fowls have been exposed to unnatural conditions of life, and their whole organisation has thus been rendered variable; but the breeder is quite indifferent to, and never intentionally selects, any modification in the skeleton. External characters, if not attended to by man, such as the number of the tail and wing feathers and their relative lengths, which in wild birds are generally constant,--fluctuate in our domestic fowls in the same manner as the several parts of the skeleton. An additional toe is a "point" in Dorkings, and has become a fixed character, but is variable in Cochins and Silk fowls. The colour of the plumage and the form of the comb are in most breeds, or even sub-breeds, eminently fixed characters; but in Dorkings these points have not been attended to, and are variable. When any modification in the skeleton is related to some external character which man values, it has been, unintentionally on his part, acted on by selection, and has become more or less fixed. We see this in the wonderful protuberance of the skull, which supports the crest of feathers in Polish fowls, and which by correlation has affected other parts of the skull. We see the same result in the two protuberances which support the horns in the horned fowl, and in the flattened shape of the front of the skull in Hamburghs consequent on their flattened and broad "rose-combs." We know not in the least whether additional ribs, or the changed outline of the occipital foramen, or the changed form of the scapula, or of the extremity of the furculum, are in any way correlated with other structures, or have arisen from the changed conditions and habits of life to which our fowls have been subjected; but there is no reason to doubt that these various modifications in the skeleton could be rendered, either by direct selection, or by the selection of correlated structures, as constant and as characteristic of each breed, as are the size and shape of the body, the colour of the plumage, and the form of the comb.

[EFFECTS OF THE DISUSE OF PARTS.

Judging from the habits of our European gallinaceous birds, Gallus bankiva in its native haunts would use its legs and wings more than do our domestic fowls, which rarely fly except to their roosts. The Silk and the Frizzled fowls, from having imperfect wing-feathers, cannot fly at all; and there is reason to believe that both these breeds are ancient, so that their progenitors during many generations cannot have flown. The Cochins, also, from their short wings and heavy bodies, can hardly fly up to a low perch.

Therefore in these breeds, especially in the two first, a considerable diminution in the wing-bones might have been expected, but this is not the case. In every specimen, after disarticulating and cleaning the bones, I carefully compared the relative length of the two main bones of the wing to each other, and of the two main bones of the leg to each other, with those of G. bankiva; and it was surprising to see (except in the case of the tarsi) how exactly the same relative length had been retained. This fact is curious, from showing how truly the proportions of an organ may be inherited, although not fully exercised during many generations. I then compared in several breeds the length of the femur and tibia with the humerus and ulna, and likewise these same bones with those of G. bankiva; the result was that the wing-bones in all the breeds (except the Burmese Jumper, which has unnaturally short legs, are slightly shortened relatively to the leg-bones; but the decrease is so slight that it may be due to the standard specimen of G. bankiva having accidentally had wings of slightly greater length than usual; so that the measurements are not worth giving.

But it deserves notice that the Silk and Frizzled fowls, which are quite incapable of flight, had their wings LESS reduced relatively to their legs than in almost any other breed! We have seen with domesticated pigeons that the bones of the wings are somewhat reduced in length, whilst the primary feathers are rather increased in length, and it is just possible, though not probable, that in the Silk and Frizzled fowls any tendency to decrease in the length of the wing-bones from disuse may have been checked through the law of compensation, by the decreased growth of the wing-feathers, and consequent increased supply of nutriment. The wing-bones, however, in both these breeds, are found to be slightly reduced in length when judged by the standard of the length of the sternum or head, relatively to these same parts in G. bankiva.

The actual weight of the main bones of the leg and wing in twelve breeds is given in the two first columns in Table 7.I. The calculated weight of the wing-bones relatively to the leg-bones, in comparison with the leg and wing-bones of G. bankiva, are given in the third column,--the weight of the wing-bones in G. bankiva being called a hundred. (7/73. It may be well to explain how the calculation has been made for the third column. In G.

bankiva the leg-bones are to the wing-bones as 86 : 54, or as (neglecting decimals) 100 : 62;-in Cochins as 311 : 162, or as 100 : 52;--in Dorkings as 557 : 248, or as 100 : 44; and so on for the other breeds. We thus get the series of 62, 52, 44 for the relative weights of the wing-bones in G.

bankiva, Cochins, Dorkings, etc. And now taking 100, instead of 62, for the weight of the wing-bones in G. bankiva, we get, by another rule of three, 83 as the weight of the wing-bones in Cochins; 70 in the Dorkings; and so on for the remainder of the third column in the table.)

TABLE 7.I. (Weights in grains.)

COLUMN 1. Actual Weight of Femur and Tibia.

COLUMN 2. Actual Weight of Humerus and Ulna.

COLUMN 3. Weight of Wing-bones relatively to the Leg-bones in comparison with these same bones in Gallus bankiva.

1. 2. 3.

Gallus bankiva -- wild male 86 54 100

1. Cochin -- male 311 162 83 2. Dorking -- male 557 248 70 3. Spanish (Minorca) -- male 386 183 75 4. Gold-Spangled Polish -- male 306 145 75 5. Game, black-breasted -- male 293 143 77 6. Malay -- female 231 116 80 7. Sultan -- male 189 94 79 8. Indian Frizzled -- male 206 88 67 9. Burmese Jumper -- female 53 36 108 10. Hamburgh (pencilled) -- male 157 104 106 11. Hamburgh (pencilled) -- female 114 77 108 12. Silk (black-boned) -- female 88 57 103

In the eight first birds, belonging to distinct breeds, in this table, we see a decided reduction in the weight of the bones of the wing.

In the Indian Frizzled fowl, which cannot fly, the reduction is carried to the greatest extent, namely, to thirty-three per cent of their proper proportional weight. In the next four birds, including the Silk hen, which is incapable of flight, we see that the wings, relatively to the legs, are slightly increased in weight; but it should be observed that, if in these birds the legs had become from any cause reduced in weight, this would give the false appearance of the wings having increased in relative weight. Now a reduction of this nature has certainly occurred with the Burmese Jumper, in which the legs are abnormally short, and in the two Hamburghs and Silk fowl, the legs, though not short, are formed of remarkably thin and light bones. I make these statements, not judging by mere eyesight, but after having calculated the weights of the leg-bones relatively to those of G.

bankiva, according to the only two standards of comparison which I could use, namely, the relative lengths of the head and sternum; for I do not know the weight of the body in G. bankiva, which would have been a better standard. According to these standards, the leg-bones in these four fowls are in a marked manner far lighter than in any other breed. It may therefore be concluded that in all cases in which the legs have not been through some unknown cause much reduced in weight, the wing-bones have become reduced in weight relatively to the leg-bones, in comparison with those of G. bankiva. And this reduction of weight may, I apprehend, safely be attributed to disuse.

To make Table 7.I. quite satisfactory, it ought to have been shown that in the eight first birds the leg-bones have not actually increased in weight out of due proportion with the rest of the body; this I cannot show, from not knowing, as already remarked, the weight of the wild Bankiva. (7/74.

Mr. Blyth (in 'Annals and Mag. of Nat. Hist.' 2nd series volume 1 1848 page 456) gives 3 1/4 pounds as the weight of a full-grown male G. bankiva; but from what I have seen of the skins and skeletons of various breeds, I cannot believe that my two specimens of G. bankiva could have weighed so much.) I am indeed inclined to suspect that the leg-bones in the Dorking, No. 2 in the table, are proportionally too heavy; but this bird was a very large one, weighing 7 pounds 2 ounces, though very thin. Its leg-bones were more than ten times as heavy as those of the Burmese Jumper! I tried to ascertain the length both of the leg-bones and wing-bones relatively to other parts of the body and skeleton: but the whole organisation in these birds, which have been so long domesticated, has become so variable, that no certain conclusions could be reached. For instance, the legs of the above Dorking c.o.c.k were nearly three-quarters of an inch too short relatively to the length of the sternum, and more than three-quarters of an inch too long relatively to the length of the skull, in comparison with these same parts in G. bankiva.

TABLE 7.II.

COLUMN 1. Length of Sternum (in inches and decimals.)

COLUMN 2. Depth of Crest of Sternum (in inches and decimals.).

COLUMN 3. Depth of Crest relatively to the length of the Sternum, in comparison with Gallus bankiva.

1. 2. 3.

Gallus bankiva -- male. 4.20 1.40 100

1. Cochin -- male. 5.83 1.55 78 2. Dorking -- male. 6.95 1.97 84 3. Spanish -- male. 6.10 1.83 90 4. Polish -- male. 5.07 1.50 87 5. Game -- male. 5.55 1.55 81 6. Malay -- female. 5.10 1.50 87 7. Sultan -- male. 4.47 1.36 90 8. Frizzled hen -- male. 4.25 1.20 84 9. Burmese Jumper -- female. 3.06 0.85 81 10. Hamburgh -- male. 5.08 1.40 81 11. Hamburgh -- female. 4.55 1.26 81 12. Silk fowl -- female. 4.49 1.01 66

In Table 7.II. in the two first columns we see in inches and decimals the length of the sternum, and the extreme depth of its crest to which the pectoral muscles are attached. In the third column we have the calculated depth of the crest, relatively to the length of the sternum, in comparison with these same parts in G. bankiva. (7/75. The third column is calculated on the same principle as explained in footnote 7/73 above.)

By looking to the third column we see that in every case the depth of the crest relatively to the length of the sternum, in comparison with G.

bankiva, is diminished, generally between 10 and 20 per cent. But the degree of reduction varies much, partly in consequence of the frequently deformed state of the sternum. In the Silk fowl, which cannot fly, the crest is 34 per cent less deep than what it ought to have been. This reduction of the crest in all the breeds probably accounts for the great variability, before referred to, in the curvature of the furculum, and in the shape of its sternal extremity. Medical men believe that the abnormal form of the spine so commonly observed in women of the higher ranks results from the attached muscles not being fully exercised. So it is with our domestic fowls, for they use their pectoral muscles but little, and, out of twenty-five sternums examined by me, three alone were perfectly symmetrical, ten were moderately crooked, and twelve were deformed to an extreme degree. Mr. Romanes, however, believes that the malformation is due to fowls whilst young resting their sternums on the sticks on which they roost.]

Finally, we may conclude with respect to the various breeds of the fowl, that the main bones of the wing have probably been shortened in a very slight degree; that they have certainly become lighter relatively to the leg-bones in all the breeds in which these latter bones are not unnaturally short or delicate; and that the crest of the sternum, to which the pectoral muscles are attached, has invariably become less prominent, the whole sternum being also extremely liable to deformity. These results we may attribute to the lessened use of the wings.

CORRELATION OF GROWTH.

I will here sum up the few facts which I have collected on this obscure, but important, subject. In Cochin and Game fowls there is perhaps some relation between the colour of the plumage and the darkness of the egg- sh.e.l.l. In Sultans the additional sickle-feathers in the tail are apparently related to the general redundancy of the plumage, as shown by the feathered legs, large crest, and beard. In two tailless fowls which I examined the oil-gland was aborted. A large crest of feathers, as Mr. Tegetmeier has remarked, seems always accompanied by a great diminution or almost entire absence of the comb. A large beard is similarly accompanied by diminished or absent wattles. These latter cases apparently come under the law of compensation or balancement of growth. A large beard beneath the lower jaw and a large top-knot on the skull often go together. The comb when of any peculiar shape, as with Horned, Spanish, and Hamburgh fowls, affects in a corresponding manner the underlying skull; and we have seen how wonderfully this is the case with Crested fowls when the crest is largely developed.

With the protuberance of the frontal bones the shape of the internal surface of the skull and of the brain is greatly modified. The presence of a crest influences in some unknown way the development of the ascending branches of the premaxillary bone, and of the inner processes of the nasal bones; and likewise the shape of the external orifice of the nostrils.

There is a plain and curious correlation between a crest of feathers and the imperfectly ossified condition of the skull. Not only does this hold good with nearly all crested fowls, but likewise with tufted ducks, and as Dr. Gunther informs me with tufted geese in Germany.

Lastly, the feathers composing the crest in male Polish fowls resemble hackles, and differ greatly in shape from those in the crest of the female.

The neck, wing-coverts, and loins in the male bird are properly covered with hackles, and it would appear that feathers of this shape have spread by correlation to the head of the male. This little fact is interesting; because, though both s.e.xes of some wild gallinaceous birds have their heads similarly ornamented, yet there is often a difference in the size and shape of feathers forming their crests. Furthermore, there is in some cases, as in the male Gold and in the male Amherst pheasants (P. pictus and amherstiae), a close relation in colour, as well as in structure, between the plumes on the head and on the loins. It would therefore appear that the same law has regulated the state of the feathers on the head and body, both with species living under natural conditions, and with birds which have varied under domestication.

CHAPTER 1.VIII.

DUCK--GOOSE--PEAc.o.c.k--TURKEY--GUINEA-FOWL--CANARY-BIRD--GOLD-FISH--HIVE- BEES--SILK-MOTHS.

DUCKS, SEVERAL BREEDS OF.

PROGRESS OF DOMESTICATION.

ORIGIN OF FROM THE COMMON WILD-DUCK.

DIFFERENCES IN THE DIFFERENT BREEDS.

OSTEOLOGICAL DIFFERENCES.