OCR Text |
Show 18 • V .A.RIATION [CnAP. I. ear, from the anhnals not being much alarmed by danger, seen1s probable. · There are many laws regulating variation, soine few of which can be dimly seen, and will be hereafter briefly mentioned. I will here only allude to what may be called correlation of growth. Any change in the embryo or larva will almost certainly entail changes in the mature anin1al. In monstrosities, the correlations between quite distinct parts are very curious ; and 1nany instances are given in Isidore Geoffroy St. I-Iilaire's great work on this subject. Breeders believe that long limbs are almost always accompanied by an elongated head. S01ne instances of correlation are quite whimsical: thus cats with. blue eyes are invariably deaf; colour and constitutional peculiarities go together, of which many remarkable cases could be given amongst animals and plants. From the facts collected by I-Ieusi~ger, it appears that white sheep and pigs are differently attected from coloured individuals by certain vegetable poisons. I-Iairless dogs have imperfect teeth; long-haired and coarse-haired animals are apt to have, as is asserted, long or many horns; pigeons with feathered feet have skin between their outer toes; pigeons with short beaks have small feet, and those with long beaks large feet. l-Ienee, if man goes on seLecting, and thus augmenting, any peculiarity, he will almost certainly unconsciously modify other parts of the stru~ture, owing to the mysterious laws of the correlation of growth. The result of the various, quite unknown, or dimly seen laws of variation is infinitely complex and diversified. It is well worth while carefully to study the several treatises published on some of our old cultivated plants, as on the hyacinth, potato, even the dahlia, &c. ; and it is really surprising to note the endless points in structure and constitution in which the varieties and subvarieties differ slightly from each other. The whole organisation seems to have become plastic, and tends to depart in some small degree from that of the parental type. Any variation which is not inherited is unimportant for us. But the number and diversity of inheritable deviations of structure, both those of slight and those of OIIAP. I.] UNDER DOMESTIC ION. 19 considerable ~hysiol?gi~al importance, is endless. Dr. Prosper Lucas s treatise, In two large volumes is the fullest and th~ best on this subject. No breeder 'doubts how st_rong IS the tendency to inheritance: like produces like is ~I~ f~ndamental be~ief: doubts have been thrown on this prinCiple by theoretical writers alone. When a deviation appears not unfrequently, and we see it in the father and child, W? ~annot tell w~ether it may not be due to the ~a~e. original cause acting on both ; but when amongst Individuals, apparently exposed to the same conditions a~y ':ery rare. deviation, due to some extraordinary com: binatlon of cucumsta~c~s, ~pp~a!~s in the parent-say, .?nee amo?gst several million Individuals-and it reappears In the ch~ld, th~ mere doctrine of chances almost compels us to attnbute 1ts reappearance t? i?herita?ce. Every one mus_t have heard o~ ca.ses of albinisin, pnckly skin, hairy bodies, &c., appearing In several members of the same fami~ Y· ~f strange and rare deviations of structure are truly Inherited, less strange and commoner deviations may be freely ad:nit~ed to be inheritable. Perhaps the correct way_of v~ewing the whole subject, would be, to look at the Inheritance of every character whatever as the rule and non-inheritance as the anomaly. ' The laws governing inheritance are quite unknown· no o~e can say why the same peculiarity in different i~diVIduals of the same species, and in individuals of different species, is sometimes inherited and sometimes not so· why the child often reverts in certain characters to it~ grandfather or grandmother or other much more rernote ancestor; why a peculiarity is often transmitted frmn one s~ to bot~ sexes, or to .one sex alone, more commonly but ~ot exclusively to the like sex. It is a fact of some little 1mportance to "!ls, that peculiarities appearing in the males of our domestic breeds are often transmitted either exclusively, or in ~ much greater degree, to males alone. A mucJ: more Important rule, which I think may be trusted, I.s that, at whatever period of life peculiarity first ~ppears, It tends to appe:=tr in the ~ffspring at a correspondmg age, though sometimes earlier. In many cases this could not be otherwise : thus the inherited peculiarities in |