soon be lost, as the males would prevail, which retained their immature dress for the longest period, and thus the character of the species would ultimately be modified.[1] If, on the other hand, the young never succeeded in obtaining a female, the habit of early reproduction would perhaps be sooner or later eliminated, from being superfluous and entailing waste of power.
The plumage of certain birds goes on increasing in beauty during many years after they are fully mature; this is the case with the train of the peacock, with some of the birds of paradise, and with the crest and plumes of certain herons, for instance, the Ardea ludovicana.[2] But it is doubtful whether the continued development of such feathers is the result of the selection of successive beneficial variations (though this is the most probable view with birds of paradise) or merely of continuous growth. Most fishes continue increasing in size, as long as they are in good health and have plenty of food; and a somewhat similar law may prevail with the plumes of birds.
Class V. When the adults of both sexes have a distinct winter and summer plumage, whether or not the male differs from the female, the young resemble the adults of both sexes in their winter dress, or much more rarely in their summer dress, or they resemble the females alone. Or the young may have an intermediate character; or, again, they may differ greatly from the adults in both their seasonal plumages.—The cases in this class are singularly complex; nor is this surprising, as they depend on inheritance, limited in a greater or less degree in three different ways, namely, by sex, age, and the season of the year. In some cases the individuals of the same species pass through at least five distinct states of plumage. With the species, in which the male differs from the female during the summer season alone, or, which is rarer, during both seasons,[3] the young generally resemble the females,—as with the so-called goldfinch of North America, and apparently with the splendid Maluri of Australia.[4] With those species, the sexes of which are alike during both the summer and winter, the young may
- ↑ Other animals, belonging to quite distinct classes, are either habitually or occasionally capable of breeding before they have fully acquired their adult characters. This is the case with the young males of the salmon. Several amphibians have been known to breed whilst retaining their larval structure. Fritz Müller has shewn ('Facts and Arguments for Darwin,' Eng. trans. 1869, p. 79) that the males of several amphipod crustaceans become sexually mature whilst young; and I infer that this is a case of premature breeding, because they have not as yet acquired their fully-developed claspers. All such facts are highly interesting, as bearing on one means by which species may undergo great modifications of character.
- ↑ Jerdon, 'Birds of India,' vol. iii. p. 507, on the peacock. Dr. Marshall, thinks that the older and more brilliant males of birds of paradise, have an advantage over the younger males; see 'Archives Néerlandaises,' tom. vi. 1871.—On Ardea, Audubon, ibid. vol. iii. p. 139.
- ↑ For illustrative cases see vol. iv. of Macgillivray's 'Hist. Brit. Birds;' on Tringa, &c., pp. 229, 271; on the Machetes, p. 172; on the Charadrius hiaticula, p. 118; on the Charadrius pluvialis, p. 94.
- ↑ For the goldfinch of N. America, Fringilla tristis, Linn., see Audubon, 'Ornith. Biography,' vol. i. p. 172. For the Maluri, Gould's 'Handbook to the Birds of Australia,' vol. i. p. 318.
