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Show 380 MORPHOLOGY. [OHAP. XIII. composed of such numerous and such extraordinarily shaped pieces of bone ~ .As . Owen has remark~d, t~e benefit derived from the y1eld1ng of the several p1eces 1n the act of parturition o~ m~mmals, will by n? 1neans explain tho same construction ln the skulls. of buds. w.hy should similar bones have been created 1n the formation of the wing and leg of a bat? used as they are for such totally different purposes~ Why should one crustacean, which has an extremely con1plex mouth formed of many parts, consequently always have fewer legs; or conversely, those with many legs have simpler mouths~ Why should the sepals, petals, sta1nens, and pistils in any individual flower, though fitted for such widely different purposes, be all constructed on the same pattern~ On the theory of natural selection, we can satisfactorily answer these questions. In the vertebrata, we see a series of internal vertebrre bearing certain processes and appendages ; in the articulata, we see the body divided into a series of segments, bearing external appendages; and in flowering plants, we see a series of successive spiral whorls of leaves. An indefinite repetition of the san1e part or organ is the common characteristic (as Owen has observed) of all low or little-modified forms; therefore we Inay readily believe that the unknown progenitor of the vertebrata possessed many vertebrre ; the unknown progenitor of the articulata, many segments ; and the unknown progenitor of flowering plants, many spiral whorls of leaves. We have formerly seen that parts many tin1es repeated are eminently liable to vary in nun1ber and structure ; consequently it is quite probable that natural selection, during a long-continued course of modifieation, should have seized on a certain number of the prin1ordially similar elements, many times repeated, and have adapted them to the most diverse purposes. And as the whole amount of modification will have been effected by slight successive steps, we need not wonder at discovering in such parts or organs, a certain degree. of fundam~ntal resemblance·, retained by the strong principle of 1n· heritance. 0BA.P. XIII.] EMBRYOLOGY. Th th 381 e great class of mollu gise the parts of one s eci sc~, though we can homolo-distinct species, we canp inJ~ ~ltl\ those of another and gies; that is, we are seldom lea ~I ~t few serial homoloor organ is homologous w'thna eh to. say that one part vidual. .And we can und~ t anot e~ In the same indiluscs, even in the lowest me rsb and }his fact; for in molfind nearly so much inde:fini: ers 0 •• the class, we do not as we find in the other great r~petltron of any one part, vegetable kingdoms. c asses of the animal and Naturalists frequently s eak f metamorphosed vertebrre . 1he . 0 th} skull as formed of phosed legs; the stamens. andJa:V~ 0 crabs as metamormorphosed leaves . but it wouran~tll~hof flowers as metabe more correct, ;s Professor I-in 1 ehe cases probably speak of both skull and vertebr~x ~y h a~ remarked, to &c.,-as having been m t ' ot Jaws and legs, other, but from some c~~%orphosed, not one from the however, use such Ian ua e onln. element. ~ aturalists, they are far from mea~in: th tYdln .a metaphorical sense: d~scent, primordial oro-ans of aan ur~n% a long co~rse of one case and legs in the other lf nn -vertebrre In the fied into skulls or · aws Yet- ave act?ally been modiof a modification of thi~ natur so st~ong Is the appearance uralists can hardly avoid e t h~ving occurred, t~at natplain signification On m mp. 0Y1~llanguage hav1ng this literally; and the .wonderfJl ~~e7 f ~he t.erms rna~ be used of a crab retainin nu c 0 e Jaws, for Instance, h::~e~ii~b~~!~ ::!:;~~i~~~r;~;hai;!h:;it:~~~f i~=~ descent from true legs or f se urn~g a long course of explained. ' rom some Simple appendage, is Embryology -It h 1 d that certain org~ns in t~e ~:J~ ·~ b~en hc~sually remarked become widel different lVI ua' w :ch when mature are in the e~r o exa and ~erve for different purposes, distinct animals y. . ctly ahke. The embryos, also, of ~lar : a bette;'1~~~~j~f 8th~e class are oft~n strikingly Circumstance mentioned b .A IS c~nnot be given, than a Y gass1z, namely, that having |