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Show 436 :MORPHOLOGY. CHAP. XIII. suppose that their common progenitor had an upper lip, mandibles, and two pair of maxillre, these parts being perhaps very simple in form; and then natural selection will account for the infinite diversity in structure and function of the mouths of insects. Nevertheless, it is conceivable that the general pattern of an organ might become so much obscured as to be finally lost, by the atrophy and ultimately by the complete abortion of certain parts, by the soldering together of other parts, and by the doubling or multiplication of others,-variations which we know to be within the limits of possibility. In the paddles of the extinct gigantic sea-lizards, and in the mouths of certain suctorial crustaceans, the general pattern seems to have been thus to a certain extent obscured. There is another and equally curious branch of the present subject; namely, the comparison not of the same part in different 1nembers of a class, but of the different parts or organs in the same individual. Most physiologists believe that the bones of the skull are homologous with-that is correspond in number and in relative connexion with-the elemental parts of a certain number of vertebrre. The anterior and posterior limbs in each member of the vertebrate and articulate classes are plainly homologous. We see the same law in comparing the wonderfully complex jaws and legs in crustaceans. It is familiar to abnost every one, that in a flower the relative position of the sepals, petals, stamens, and pistils, as well as their intimate structure, are intelligible on the view that they consist of metamorphosed leaves, arranged in a spire. In monstrous plants, we often get direct evidence of the possibility of one organ being transformed into another; and we can actual!! s e in embryonic crustaceans and in many other animals, and in flowers, that organs, which when mature CHAP. XIII. MORPHOI~OGY. 437 become extremely· di.cu£'e rent are at a 1 growth exactly alike. ' n ear Y stage of How inexplicable are these £ t ~iew of creation! Why should : s on_ the ordinary m a box composed of suI e bram be enclosed ordinarily shaped pieces ~/ :~~;rous and such extramarked, the benefit der·I ve d f rom thA s O. wlde' n has re-separate pieces in the act of p t . . e yie Ing of the b ar untwn of rna 1 il Y no means explain the mma s, w 1 ?f birds. Why should si:~a: ~nstruction in the skulls ln the formation of the . odnes have been created th wing an leg of a b t d ey are for such to tall d. :ffi a , use as should one crustacean wh! h ~ erent purposes? Why mouth formed of man' lC as an extremely complex fewer legs; or conve~s;l~rtihconse~u~ntly always have simpler mouths? Why shoul~ethwit many legs have mens, and pistils in an . d. . d e sepals, petals, stafor such widely differ~n~n IVI ual flower, though fitted on the same pattern? purposes, be all constructed On the theory of natural sel t. . answer these questions I th ec wn, we can satiSfactorily of internal vertebrre b . .n e vertebrata, we see a series dages . in the art. 1 etaring certain processes and appen- ' wu a a, we see the bod di 'd d . series of segments b . Y VI e mto a flowering plants 'weearmg exter,nal appendages ; and in whorls of leaves.' An ~:~e~ ~ene.s of. ~uccessive spiral part or organ I·s th nite repetition of the same e common ch t · · has observed) of all I I' arac eristic (as Owen ~ ow or 1ttle-modifi d ~ h •ore we may readily b li h e .orms ; t ere-of t.he vertebrata poss:ss:~e t at the unknown progenitor progenitor of the t' I many vertebroo; the unknown k ar 1cu at.a many un nown progenitor of fl ' . segments ; and the whorls of leaves W h ~wenng plants, many spiral t I.m es repeated · e av. e 10rmerly se en tha t parts many and structure. are eminently.Ii~ble to vary in number ' consequently It Is quite probable that |