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Show 394 RUDIMENTARY ORGANS. [Cn.A.P. XIII. injurious to the system; but can we supp~se. t~at the minute papilla, which often represents the pistil m .male flowers, and which is formed merely of cellu~ar tissue, can thus act? Can we suppose that the formation of rudilnentary teeth which are subse9.uently abso;bed, can be of any service to the rapidly growing .embryonic calf by tl;e excretion of precious phosphat~ of hme ? ~hen a ~an s fingers have been amputated, unperfect nails sometnnes appear on the stumps: I could as soon believe that these vestiges of nails have appeared, not fron1 unknown laws of growth, but in order to excrete horny n1atter, as that the rudin1entary nails on the fin of the 1nanatee were formed for this purpose. . . . . . On 1ny view of desc~nt ~Ith modification, the ongin of rudimentary organs IS si:nple. We h~ve plent:y of cases of rudimentary organs 1n our domestic produ~twns, -as the stump of a tail in tailless breeds,-the vestige of an ear in earless breeds,-the reappearance of minute dangling horns in hornle~s breeds of ~attle, more especially, according to You~tt, In you~g animals,-and the state of the whole flower In the cauh:flower. We often see rudiments of various parts in mons.ters. But I. ~oubt whether any of these cases throw hght on the ongin of rudin1entary organs in a state of nature, further than by showing that rudiments can be produced ; for I doubt whether species under nature ever under$o abrupt ch an ge~. I believe that disuse has been the main agency ; that It has led in successive generations to the gradual ! eduction ·of various organs, until they have b.ecome .ruthn;~ntary -as in the case of the eyes of animals Inhabiting dark caverns and of the wings of birds inhabiting oceanic islands which have seldom been forced to take flight, and have ~ltimately lost the power of flying. Again: ~n organ useful under certain condit~ons might beco~~ InJUrious under others, as with the wings of beetles hving on small and exposed islands ; and in this case natural s~le?tion would continue slowly to reduce the organ, until It was rendered harmless and rudimentary. Any change in function, which can be .. effected by insensibly small sten~, is within the power ot natural se- CHAP. XIII.] RUDIMENTARY ORGANS. 395 lecti.on; so that a~ o.rg~n rendered, during changed habits of hfe, .n.seless or InJurious for one purpose, might easily b~ modified an~ used for another purpose. Or an organ might be retmned for one alone of its former functions. An. organ? w:hen rendered useless, may well be variable, for Its vanabons. cannot .be c~ecked by natural selection. At whatever period of hfe disuse or selection reduces an organ, a~d this will .generally be when the being has come to J?atu~Ity and to Its full p~wers of action, the principle of Inhentance at corresponding ages will :reproduce the organ in its reduced state at the same age and consequently will seldom affect or reduce it in th~ embryo. Thus we can understand the greater relative size of rudimentary organs in the embryo, and their lesser relative size in the adult. But if each step of the process of reduction were to be inherited, not at the corresponding age but at an extrmnely early period of life, (as we have good reason to believe to be possible,) the rudimentary part would tend to be wholly lost, and we should have a case of complete abortion. The principle, also, of economy, explained in a former chapter, by which the materials forming any part or structure, if not useful to the possessor, will be saved as far as is possible, will probably often come into play; and this will tend to cause the entire obliteration of a rudimentary organ. As the presence of rudimentary organs is thus due to the tendency in every part of the organisation, which has long existed, to be inherited-we can understand, on the genealogical view of classification, how it is that systematists have found rudimentary parts as useful as, or even ~ometimes more u~eful than, parts of high physiological Importance. Rudimentary organs may be compared with . the letters in a word, still retained in the spelling, but become useless in the pronunciation, but which serve as a clue in seeking for its derivation. On the view of descent with modification, we may conclude that the existence of organs in a rudimentary, imperfect, and useless condition, or quite aborted, far from presenting a strange difficulty, as they assuredly do on the ordinary doctrine of creation, |