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Show 120 LAWS OF VARIATION. (CIIAP. V CHAPTER V. LAWS OF VARIATION. d disuse comb m. e d with natural seCl ection ; Effects of external conditions-Use a~ tisati~n-Correlation of growth- ompen~ organs of flight and of vision-Ac; ~~a correlations-Multiple, rudimentary, an sation and economy of growth- a se ts developed in an unusual manner are lowly organised structures variable-Par riable than generic: secondary sexual highly variable: specific characters more vanus vary in an analogous manner- Recharacters variable-Species of the same ge versions to long lost characters-Summary. . oken as if the variations-so I H.A. vE hitherto sometlm~s sp . bei'ngs under domes- cornmon and mu1 t l· f ,o rm In org.a ntihc ose in a state of nature tication, and in a lesser degrT~~n f course is a wholly in- had been due to chan?e. IS, to ackno~ledge plainly correct expressi·o n ' but It servf es coh particular vari.a ti·o n. our ignorance of. the .cause o a~amuch the function of the Some authors beheve It to ~e . dividual differences, or reprod~ctive sy~te.m to fr~r~~:u;~ as to make t~~ child very ~hght deviatHBS to the much' greater variabihty, . as like Its parents. f cy of monstrosities under dowell as the greatm: r~quen han under nature, leads me to mestication or c~lt~vatlon, t ructure are in some way due believe that deviations 1-t~t of life to which the parents to the nature of the con 1 lOllS have been exposed during and their more remote ancestors k d . the first chapter 1 t" s I have rernar e m severa genera lOll .1 f facts which cannot be here -but a long cat a ogue o t how the truth of the remark given, would be nece~sary ~ s . s eminently susceptible -that the ~·eproductlJ·~· sys ef l~fe. and to this system to changes ~ the cor; 1 l~ons ~n the' arents, I chiefly_ atbeing functionally dlstur ~e~. ndiBon of the offsprmg. tribute the varying or p als lf coents seem to be affected The male and female sexua e em 0RA.P. V.] LAWS OF VARIATION, 121 before that union takes place which is to form a new being. In the case of "sporting" plants, the bud, which in its earliest condition does not apparently differ essentially from an ovule, is alone affected. But why, because the reproductive systen1 is disturbed, this or that part should vary more or less, we are profoundly ignorant. N evertheless, we can here and there dimly catch a faint ray of light, and we may feel sure that there must be some cause for each deviation of structure, however slight. How n1uch direct effect difference of climate, food, &c., produces on any being is extremely doubtful. My impression is, that the effect is extremely small in the case of animals, but perhaps rather n;wre in that of plants. We may, at least, safely conclude that such influences cannot have produced the many striking and complex coadaptations of structure between one organic being and another, which we see everywhere throughout nature. Some little influence may be attributed to climate, food, &c. : thus, E. Forbes speaks confidently that shells at their southern limit, and when living in shallow water, are more brightly coloured than those of the same species further north or from greater depths. Gould believes that birds of the same species are more brightly coloured under a clear atmosphere, than when living on islands or near the coast. So with insects, Wollaston is convinced that residence near the sea affects their colours. Moquin-Tandon gives a list of plants which when growing near the seashore have their leaves in some degree fleshy, though not elsewhere fleshy. Several other such cases could be given. The fact of varieties of one species, when they range into the zone of habitation of other species, often acquiring in a very slight degree some of the characters of such species, accords with our view that species of all kinds are only well-marked and permanent varieties. Thus the species of shells which are confined to tropical and shallow seas are generally brighter-coloured than those confined to cold and deeper seas. The birds which are confined to continents are, according to Mr. Gould, brighter-coloured than those of islands. The insect-species confined to sea- 6 ( |