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Show 1874.] MOLOTHRI OF BUENOS AYRES. 171 The Patagonian Thrush (Turdus falklandicus) is not a singing bird; occasionally, however, in spring, an individual is heard to sing. I believe the singing in this case is a recurrence to a disused habit, because most Thrushes sing, also because the La-Platan Thrushes never sing in winter or during high winds in summer (high winds prevail all summer in Patagonia, though the winter is calm), also because the song of T. falklandicus, when it does sing, is like a laboured imitation of the song of T. rufiventris of L a Plata, the species which it most closely resembles. The following also appears to be an example of recurrence to an ancestral instinct. A physiological study of the Ophidians has, I believe, afforded some reasons for supposing that these reptiles or their progenitors were all originally aquatic in their habits. The extreme readiness with which land-snakes enter the water, their apparent fondness for it, as if it were their native element, and the facility with which they swim give greater strength to the supposition. Last summer (December 1872) I noticed a Coronella anomala on the border of a stream where I was fishing, with its body so much distended that, curious to learn what it had swallowed, I killed and opened it. There were in it fifteen little fishes, varying in size from 2 to 3£ inches in length. A few of the fishes had begun to decompose ; but they had evidently all been taken that day, showing in what marvellous perfection this individual possessed the fishing instinct. Yet the C. anomala (our commonest snake, though until lately un-described) abounds everywhere on dry elevated plains where there is never any standing water. This snake was a full-grown male 1 4| inches long; the female differs in colour, and is much larger. From the number of leaves that had been swallowed along with the fishes it was evident that the snake had lain among the rotting leaves of the floating water-lilies to watch for its prey ; and indeed the colour of the body, the stem-like raised neck, and still watchful habit seem to adapt it for preying on fish in the water rather than on mice, birds, &c. on dry land. The last case of recurrence, or what appears such, will probably seem less obvious than the preceding ones; it refers to Molothrus bonariensis, and a strange purposeless habit of that species already mentioned in a former paper. Before and during the breeding- season the females, sometimes accompanied by the males, are seen continually haunting and examining the domed nests of some of the Dendrocolaptidse. This does not seem like a mere freak of curiosity, but their persistence in the habit is precisely like that of birds that habitually make choice of such breeding-places. It is most surprising that they never do in reality lay in such nests, except when the side or dome has been accidentally broken enough to admit the light into the interior. Whenever I set up boxes in m y trees, the first bird to visit them is the female M. bonariensis. Sometimes one will spend half a day loitering about and inspecting a box, repeatedly climbing round and over it, and always ending at the entrance, into which she peers curiously and, when about to enter, starting back as if scared at the obscurity within. But after retiring a 12* |