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Show 184 SEXU A.L SELECTION : BIRDS. PART If. are marked with feeble stripes or rows of spots,. a1:u as many allied species both young .and o~cl are sim1larly marked, no naturalist, who believes m the g~·adual evolution of species, will doubt that the progemtor of the lion and pnma was a striped animal, the )~Oung having retained vestiges of the stripes, like :be k1ttens of black cats, which when grown np are not m the least striped. Many species of deer, which w.hen m~ture are not spotted, are whilst young covered with white spots, as are likewise some few species in their adult state. So again the young in the whole family o~ pigs (Suidro), and in certain rather distantly-allied ammals, such as the tapir, are marked with dark longitudina! stripes ; but here we have a character apparently derived from an extinct progenitor, and now preserved by the young alone. In all such cases the old have had their colours chanrred in the course of time, whilst the young have remained but little altered, anu this has been effected through the principle of inheritance at corresponding ages. 'fhis same principle npplies to many birds belonging to various groups, in which the young closely resemble each other, and differ much from their respective adult parents. 'fhe young of almost. all the Gallinaccro, and of some di!:itantly-allied birds sueh as ostriches, are whilst covered w'ith down longitudinally striped ; but this character points back to a state of things so remote that it hardly concerns us. Young cross-bills· (Loxia) have at first straight beaks like those of other finches, and in their immature striated plumage they resemble the mature redpole and female siskin, as well as the young of the goldfinch, greenfinch, and some other u.llied species. The young of many kinds of buntings (Emberiza) resemble each other, and like-· wise the adult state of the common bunting, E. mili- CHAP. XVI. INHERITANCE, LIMITED llY AGE. 185 a1·ia. In almost the whole large group of thrushes the young have their breasts spotted-a chnractei· which is retained by many species throughout life, but is quite lost by others, as by the T~wdus migratorius. So again with many thrushes, the feathers on the back are mottled before they are moulted for the first time, and this character is retained for life bv certain eastern species. The young of many species ;f shrikes (Lanius), of some woodpeckers, and of an Indian pigeon (Ohaleophaps lndieus), are transversely striped on the under sm-faco; and certain allied species or genera when adult are similarly marked. In some clo ely-allied and resplendent Indian cuckoos (Chrysococcyx), the species when mature differ considerably from each other in colour, but the young cannot be dis-· tinguished. The young of an Indian goose (Sarkidiornis rnelanonotus) closely resemble in plumage an allied genus, Dendrocygna, when mature.1 Similar facts will hereafter be given in regard to certain herons. Young black grouse (Tetrao tetrix) reAemble the young as welL as the old of certain other species, for instance the reel grouse or T. seotieus. Finally, as Mr. Blyth, who has attended closely to this subject, has well remarked, the natural affinities of many species are best exhibited in their immature pluiuage ; and as the trne affinities of all organic beings depend on their descent from a common progenitor, this remark strongly confirms the belief that the immature plumage approximately shews us the former or ancestral condition of the species. 1 In regard to thrushes, shrikes, nn<.l woodpeckers, sec 1\lr. Blyth, in Chn~·lesworth'~ 'Mag. of Nat. llist.' vol. i. 1837, p. 304; also footnote to l11s ~ranslatwn of Cuvicr's 'Rcgne Animal,' p. 159. I give the case of Loxw. from Mr. Blyth's information. On thrushes, sec also Audubon, 'Omith. Biography,' vol. ii. p. 195. On Chrysococcyx and Chn.lcnphaps, Blyth, as quoted in Jordon's • Birds of India,' vol. iii. p. 485. On Sarkidiomis, Blyth, in 'Ibis,' 1867, p. 175. |