OCR Text |
Show 270 FOWLS. CHAP. Vll. Cochins and Silk-fowl. . The colour of the plumage and the form of tho comb are in most breeds, or oven sub-br eels, eminently fixed characters; lmt in Dorlcings the ·o points have not been attend d to, and are variable. ·when any modification in the sl.:clcton is xclat d to some external character which man values, it has h n, uninteutionally on his part, acted on by selection, and has become more or less fixed. W o so this in the wonderful protubcranco of the sknll, which supports the crest of feathers in Poli h fowls, and whieh by correlation has affected other parts of the skull. We sec the same result in the two protuberances which support the homs in the horned fowl, and in the flattened hape of the front of the skull in llamburghs consequent on their flattened and broad " rose-combs." vVo know not in the least whether additional ribs, or the changed outline of tho occipital foramen, or the changed form of the scapula, or of the extremity of th furcula, arc in any way correlated with other structures, or have aris n from the changed conditions and habits of life to which our fowls have been subj ctcd; but there is no rca. on to doubt that these various mocMications in the skeleton could be rendered, cith r by direct selection, or by the selection of correlated structures, as constant and as characteristic of each breed, as arc the size and shape of the body, the colour of tho plumage, and the form of the comb. Effects of the Disuse of Parts. Judging from tho habits of our European gallinaceous birds, OaZZ.us banldvrL in its native hauntR wouJd usc its lcgB and wings more than do our domestic fowls, which mrcly fly except to their roosts. Tho Silk and tho :F'J:izzl d fowls, from having imperfect wing-feathers, cannot fly at all; and there iB rca on to believe that both these brccdR arc ancient, so that their progenitors during many generations cannot have flown. Tho Cochins, al. ·o, from their short wings and heavy bodicR, can hardly fly 11p to a low porch. Therefore in these brccdB, especially in the two first, a considerable diminution in tho wing-bones might have boon expected, but this is not the ca. c. In every specimen, after disarticulating and cleaning tho bones, I carefuJly compared tho relative length of the two main bones of tho wing to each other, and of the two main bones of tho leg to each other, with those of G. ban kiva; and it was smprising to sec (except in tho case of tho tarsi) how exactly the same relative length had been retained. This fact is cmious, from showing how truly the proportions of an organ may bo inherited, although not fully exercised dm·ing many generations. I then compared in several breeds tho C IIAL'. VJI. TilE EFFECTS OF DISUSE. 271 len~th of tho fomu:r and tibia with tho humerus and ulna, and liJmwiso those s~mo bones w1th those of G. banlcivct; tho result was that the wingbones m all the breeds (except tho Burmese Jumper which has unnatuxally Bhort lcg.B) arc. slightly shortened relatively to tho leg-bones. but tho dec. rease JS. so sbg. ht that it may bo due to tl.1 o s t and ard spccr·r non' of 0. ban/,;wa havmg acCidentally had wings of slightly greater length than usu.al; so that th? mcasmcmcnts arc not worth giving. But it deserves n?hco that th? SI!k and Frizzled fowls, which are q1uto incapable of fl1ght, ha~ t~1cu· wmgs less reduce~ relatively to their legs than in almost any oth~r breed.! We have seen With domesticated pigeons that tho bones of the. wtl mg. s· arc. somd ew: hat reduced in. len. gt.h ' whi·l st tho pr·1·m ary 1"" ea tl1 ors arc m 10r mc1casc ill length, and .1t 1s Just possibl th h t . b bl tl t · th s· · e, oug no piO-1 a n-ctl, 1fa 1m · c 1ln: and Frizzled fowls any tendency to c1 c crcaso r·n tho enn 1 o t 10 wm?-boncs from disuse may have been checked through the law of comp.c nsatwn, by tho decreased growth of' tl1o wm· g-1.re a thc rs and consequent mcrca cd s~pply of nutriment. Tho wing-bones, howcv~r in both these breeds, arc found to bo slightly reduced in length when jud~ed by the st·111~ard of the length of tho sternum or head, relative! to these same parts Ill a. banlciva. y b .T hde a· ctua· l we·i ght of the main bones of the leg """ nd w· mg m· t we 1v c rcc s IS g1v~n m ~ho two. first columns in tho following table. The calc· u, lated· hw mght of tho w.m g-boncs relatively to the 1C Coi '-b ones, m· com-panson Wlt tho .log an~ wmg-~oncs of G. brtnlcivcL, arc given in the third column,---:thc wmght of the wmg-boncs in G. banlciva being called hund.rcd/3 a 'J'ABLE 1. Names of Dreed;. Gallus bnnkiva .. .. wild malo 1 Corltin 2 Dm·king : : :: .. malo 3 .. male 4 Spanish (Minorra) .. male 5 Golu Spangled Polish male Gnme, black-breasted malo 6 Malay.. .. .. .. female 7 Sultan .. .. .. .. male 8 Indian Frizzled 9 Burmese J umpcr · · :: male 10 female 11 liamburgh (ponci ll e<l~ malo 12 Hamburgh (pencilled female Silk (black-boned) .. femnJo i3 It may be well to oxplnin how the calculation lms been made for tho third column. In G. bankiva the log-Lonos A<·tual I Weight of Wing- Actmtl bone; r~laU v ly t.o Weight of ''>'eight of tho Leg-bone.;, in Femur and Humerus and 'comparison with Til.lia. U Ina. these sume I.Joncs i11 G. hanklvn. ------ Grains ... Grains. 8G 54 100 311 IG2 8B 557 248 70 38G 183 75 306 145 75 2D3 143 77 231 116 80 189 94 7D 206 88 67 53 36 108 157 104 106 114 77 lOR 88 57 103 are to tho wing-bones as 86 : 54, or as (neglecting decimals) 100 : G2;- in Coohius as 311 : 162, or as 100 : 52;- |