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Show 16 VARIATION [OHAP. I. under confinement; and when, on the other han~, we see individuals, though taken young from a state. of nature, perfectly tamed, long-lived, and he~lthy (o~ which I co~ld give numerous instances), yet having thmr reproductive system so seriously affected by unper.ceived cal!-ses as to fail in acting, we, need not be surpnse_d at this ~ystem, when it does act under confinement, acting not quite regularly, and producing offspring not perfectly like their parents or variable. Sterility has been said to be the bane of horticulture ; but on this view we owe variability to the same cause which produces sterility ; and variability is the source f all the choicest productions of the garden. I .may add, that as some organisms will breed most freely under the most unnatural conditions (for instance, the rabbit and ferret kept in hutches), showing that their reproductive system has not been thus affected; so will some animals and plants withstand d01nestication or cultivation, and vary very slightly-perhaps hardly Inore than in a state of nature. A long list could easily be given of " sportin~ plants;" by this term gardeners mean a single bud or offset, which suddenly assumes a new and sometimes very different character from that of the rest of the plant. Such buds can be propagated by grafting, &c., and sometimes by seed. These "sports"are extremely rare under nature, but far from rare under cultivation ; and in this case we see that the treatment of the parent has affected a bud or offset, and not the ovules or pollen. But it is the opinion of most physiologists that there is no essential difference between a bud and an o.vule in their earliest stages of formation ; so that, in fact, " sports " support my view, that variability may be largely attributed to the ovules or pollen, or to both, having been affected by the treatment of the parent prior to tbe act of conception. These cases anyhow show that yariation is not necessarily connected, as some authors have supposed, with the act of generation. Seedlings from the same fruit, and the young of the same litter, sometimes differ considerably from each other, Cn.AP. I .] UNDER DOMESTIC..LtTION. 11 though both the young and the parents, as Muller has remarked, h_aye appa;ently bee:r:t exposed to exactly the same .conditions of hfe; and. t~IS sho'Ys ho": unimportant the direct effects of the conditions of hfe are In comparison wit~ the laws of reproduct~on, and of growth, and of inheritance; for had the action of the conditions been di· rect, if a~y ~f the young had varied, all would probably ~ave varied In the san;e . manner. To judge how much, In the case of any vanation, we should attribute to the ~rect action ?f heat,_ m~isture, light, food, &c., is most d!:fficult: my Impression Is, that with animals such agenCies have pro~uced very little direct effect, though ap- .p~rently more m th~ case of plants. Under this point of VIew, Mr. Buckman s recent experiments on plants seem extremely valuable. When all or nearly all the individuals exposed to certain conditions are aff'ected in the same way, the change at first appears to be directly due to such conditions ; but in some cases it can be shown that quite opposite conditions produce similar changes of structure: N everth~less some slig:ht amo';nt of cliange may, I think, be attributed to the direct action of the conditions of life--as, in some cases, increased size from amount of food, colour from particular kinds of food and from light and perhap.s the thickness of fur from climate. ' H~bit al~o has a decided influence, as in the period of flowenng With plants when transported from one climate to another. In animals it has a more marked. effect· for instance, I find in the domestic duck that the bones of the '!ing weigh less and the bones of the leg more, in proporti? n to the whole skeleton, than do the same bones in the Wil~ duck; and I presum~ that this change may be safely attri~uted to the do_mest~c duck flying much less, and wa~kmg more, than Its wild parent. The great and inherite~ development of the udders in cows and goats in c~untries where they are habitually milked, in comparison -yvith the state of these organs in other countries, is another 1nstance of the effect of use. Not a single domestic ani~ al can be named which has not in some country dro'oplng ears ; and the view suggested by some authors that the drooping is due to the disuse of the muscles df the |
