"It is probable that _disuse has been the main agent in rendering organs rudimentary_," or in other words that Lamarck was quite right--nor does one see why if disuse is after all the main agent in rendering an organ rudimentary, use should not have been the main agent in developing it--but let that pass. "It (disuse) would at first lead," continues Mr. Darwin, "by slow steps to the more and more complete reduction of a part, until at last it became rudimentary--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 by beasts of prey to take flight, and have ultimately lost the power of flying. Again, an organ useful under certain conditions, might become injurious under others, _as with the wings of beetles living on small and exposed islands_;"[372] so that the rudimentary condition of the Madeira beetles' wings is here set down as mainly due to disuse--while above we find it mainly due to natural selection--I should say that immediately after the word "islands" just quoted, Mr. Darwin adds "and in this case natural selection will have aided in reducing the organ, until it was rendered harmless and rudimentary," but this is Mr. Darwin's manner, and must go for what it is worth. How refreshing to turn to the simple straightforward language of Lamarck. "Long continued disuse," he writes, "in consequence of the habits which an animal has contracted, gradually reduces an organ, and leads to its final disappearance.... "Eyes placed in the head form an essential part of that plan on which we observe all vertebrate organisms to be constructed. Nevertheless the mole which uses its vision very little, has eyes which are only very small and hardly apparent. "The _aspalax_ of Olivier, which lives underground like the mole, and exposes itself even less than the mole to the light of day, has wholly lost the use of its sight, nor does it retain more than mere traces of visual organs, these traces again being hidden under the skin and under certain other parts which cover them up and leave not even the smallest access to the light. The Proteus, an aquatic reptile akin to the Salamander and living in deep and obscure cavities under water, has, like the aspalax, no longer anything but traces of eyes remaining--traces which are again entirely hidden and covered up.[373] "The following consideration should be decisive.