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Show 130 J.JAWS OF VARIATION. [0HAP, V. . . . f dl'ng kidney-beans differences In the constitution o see ~1' ~hed how much ever appear, for an acc?unt has been pu ~than others. n1ore hardy some seedlings appeared to bl d that habit On the whole, I think we may cone u e ~nsiderabl~ usc, and disuse, have, in some cases, pl~yet~ a c nd of the Part in the modification of the constitu IOn.ka f structure of vari.o us organs .' b u t that thbe. e1d1 ects· t ho usde and disuse have often been largely com In~ wf.' ai~ sometimes overmastered by, the natural selection o Inn a e differences. Correlation of Growtl'll.-1 m~an by this exp~essi?n that the whole organisation is so tied t~gether ~u~Ing I_ts growth and development, that when shght variations In any one part occur, and are accum~lated thro?-g~1 natur~l selection other parts become modified. Th1s IS a vei Y importa~t subject, most imperfe?tly ~1nderstood. The most obvious case is, that modrficat1ons ac~um.ulated solely for the good of the young or larva, will, It m~y safely be concluded, affect the structure. of the ad_ult ; In the same n1anner as any malconformation aff~ctl~g the early embryo, seriously affects the whole or~arusatlon of the adult. The several parts of the body w~1ch ar~ homoloO'ous, and which, at an early en:bryonic penod, are alfice, semn liable to vary in an allied manne~: ~e see this in the right and left sides of th.e body varying 1n tl;e same manner ; in the front and h1nd legs, and eve~ In the jaws and limbs varying together, for the lower ,1aw is believed to be h~mologous with the limbs. These tendencies, I do not doub~, may be mastered rr:ore or less completely by natural selection ·: thus a _family of. sta~s once existed with an antler only on one. s1d~ ; and If this had been of any great use to the breed It m1ght _Probably have been rendered permanent by natural selection. Homologous parts, as l~as. been remar~ed by some authors, tend to cohere; this IS often seen 1n mon.strous plants· and nothing is more common than the un1on of homol~gous parts In normal structures, as the union of the petals of the corolla into a tube. Ha:rd. part~ seem to affect the form of adjoining soft parts ; It IS beheved by OnA.P. V.J OORREL.ATION OF GROWTH. 131 some authors that the diversity in the shape of the pelvis in birds causes the remarkable diversity in the shape of their kidneys. Others believe that the shape of the pelvis in the human mother influences by pressure the shape of the head of the child. In snakes, according to Schlegel, the shape of the body and the·manner of swallowing determine the position of several of the most important viscera. The nature of the bond of correlation is 'very frequently quite obscure. M. Is. Geoffroy St. Hilaire has forcibly remarked, that certain malconformations very frequently, and that others rarely coexist, without our being able to assign .any reason. What can be more singular than the relation between blue eyes and deafness in cats, and the tortoise-shell colour with the female sex ; the feathered feet and skin between the outer toes in pigeons, and the presence of more or less down on the young birds when first hatched, with the future colour of their plumage; or, again, the relation between the hair and teeth in the naked Turkish dog, though here :probably homology comes into play ? With respect to this latter case of correlation, I think it can hardly be accidental, that if we pick out the two orders of mammalia which are most abnormal in their dermal covering, viz. Cetacea (whales) and Edentata (armadilloes, scaly ant-eaters, &c.), that these are likewise the most abnormal in their teeth. I know of no case better adapted to show the importance of the laws of correlation in modifying important structures, independently of utility and, therefore, of natural selection, than that of the difference between the outer and inner flowers in some Compositous and Umbelliferous plants. Every one knows the difference in the ray and central florets of, for instance, the daisy, and this difference is often accompanied with the abortion of parts of the flower. But, in some Compositons plants, the seeds also differ in shape and sculpture; and even the ovary itself, with · its accessory parts, differs, as has been described by Cassini. These differences have been attributed by some authors to pressure, and the shape of the seeds in the ray-florets in some Compositre countenances |