In July they set sail again for Monte Video, where the important question of climate and vegetation began to interest young Darwin's mind. Uruguay is almost entirely treeless; and this curious phenomenon, in a comparatively moist sub-tropical plain-land, struck him as a remarkable anomaly, and set him speculating on its probable cause. Australia, he remembered, was far more arid, and yet its interior was everywhere covered by whole forests of quaint indigenous gum-trees. Could it be that there were no trees adapted to the climate? As yet, the true causes of geographical distribution had not clearly dawned upon Darwin's mind; but that a young man of twenty-three should seriously busy himself about such problems of ultimate causation at all is in itself a sufficiently pointed and remarkable phenomenon. It was here, too, that he first saw that curious animal, the Tucutuco, a true rodent with the habits of a mole, which is almost always found in a blind condition. With reference to this singular creature, there occurs in his journal one of those interesting anticipatory passages which show the rough workings of the distinctive evolutionary Darwinian concept in its earlier stages. 'Considering the strictly subterranean habits of the Tucutuco,' he writes, 'the blindness, though so common, cannot be a very serious evil; yet it appears strange that any animal should possess an organ frequently subject to be injured. Lamarck would have been delighted with this fact, had he known it, when speculating (probably with more truth than usual with him) on the gradually acquired blindness of the Aspalax, a gnawer living under the ground, and of the Proteus, a reptile living in dark caverns filled with water; in both of which animals the eye is in an almost rudimentary state, and is covered by a tendinous membrane and skin. In the common mole the eye is extraordinarily small but perfect, though many anatomists doubt whether it is connected with the true optic nerve; its vision must certainly be imperfect, though probably useful to the animal when it leaves its burrow. In the Tucutuco, which I believe never comes to the surface of the ground, the eye is rather larger, but often rendered blind and useless, though without apparently causing any inconvenience to the animal: no doubt Lamarck would have said that the Tucutuco is now passing into the state of the Aspalax and Proteus.' The passage is instructive both as showing that Darwin was already familiar with Lamarck's writings, and as pointing out the natural course of his own future development.