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Fritz Müller on Brazil Kitchen Middens, Habits of Ants, &c.

[MR. CHARLES DARWIN has kindly sent us for publication the following letter, addressed to him by Herr Fritz Müller, the well-known naturalist, brother of our contributor, Dr. Hermann Müller, and who has for so long been devoting himself to natural history researches in Brazil.]

My dear Sir,—In Desterro I met with two young men (M. Charles Wiener, of Paris, and M. Carl Schreiner, from the National Museum of Rio) who, by order of the Brazilian Government, were examining the "Sambaquis" of our province. I accompanied them in some of their excursions. These "Sambaquis," or "Casqueiros," are hillocks of shells accumulated by the former inhabitants of our coast; they exist in great number, and some of them are now to be found at a distance of several miles from the sea-shore, though originally they were, of course, built near the spot where the shells lived. Some are of considerable size; we were told that a Sambaqui on a little island near San Francisco had a height of about 100 metres; but the largest I have seen myself did not exceed 10 or 12 metres. As to the shells of which they are composed, the Sambaquis may be divided into three classes, viz.: (1) Sambaquis, consisting of many different species of bivalve and univalve shells (Venus, Cardium,

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Lucina, Arca, Ostrea, Purpura, Tritonium, Trochus, &c.), all of which are at present living in the neighbouring sea. (2) Sambaquis, consisting almost exclusively of a small bivalve shell, the "Birbigãs" of the Brazilians (Venus flexuosa?), exceedingly common in shallow bays or salt-water lagoas, the bottom of which is of mixed mud and sand. (3) Sambaquis, consisting exclusively of a species of Corbula, which I have not yet seen in a living state; all the Brazilians also, whom I asked, and who are perfectly acquainted with any edible animal of their marine fauna, are unanimous in affirming that this shell does not live now on our coast. From one of these Corbula-Sambaquis I obtained a specimen of a small Melampus, which I have found living near the mouth of some rivulets, where fresh and salt water are mingling in ever-varying proportions. When the lowlands of the Lower Itajahy and some of its tributaries were as yet beneath the level of the sea, they would have formed a large estuary, and here probably the Corbulæ lived. The fragments of human skulls which we found in one of these Corbula-Sambaquis were of truly astonishing thickness, whereas those I have seen from other Sambaquis are hardly thicker than our own. Among the tools which are to be found in the Sambaquis, stone-axes are by far the most frequent. But as M. Wiener will probably soon publish a full account of his researches, I will now no longer dwell on this subject.

Some time ago I sent to Germany for publication a note on the relation between our Imbauba trees (Cecropia) and the ants which inhabit their hollow stem. As there may be some delay in publishing, I will give you a short abstract. Mr. Belt has already stated that the ants farm scale-insects in the cells of the Imbauba stem, and he believes that their presence must be beneficial. This is no doubt the case; for they protect the young leaves against the leaf-cutting ants (Oecodoma). Now there is a wonderful contrivance by which, as in the case of the "bull's-horn acacia," the attendance of the ants at the right time and place is secured. At the base of each petiole there is a large flat cushion, consisting of most densely-crowded hairs, and within this cushion a large number of small white pear-like or club-shaped bodies (specimens inclosed) are successively developed, which, when ripe, emerge at the surface of the cushion, like asparagus on a bed, and are then greedily gathered by the ants and carried away to the nest. The object of the dense hair-cushion appears to be (1) to secure to the young club-shaped bodies the moisture necesary for their development; and (2) to prevent the ants from gathering the unripe bodies. In most cases it is by honey-secreting glands that the protecting ants are attracted; now Mr Belt observed ("Nicaragua," p. 225) that the honey-glands on the calyx and young leaves of a Passion-flower were less attractive to the ants than were the scale-insects living on the stems; this would most likely be the case with the Imbauba, and it is probable that the use of the little pear-shaped bodies is to form an attraction stronger than that of the scale-insects, and thus to secure the attendance of the protective ants on the young leaves. As far as I could make out, the club-shaped bodies consist mainly of an albuminous substance. The ant colonies are founded by fertilised females, which may be found frequently in the cells of young Imbauba plants. Each internode has on the outside, near its upper end, a small pit where the wall of the cell is much thinner than anywhere else, and where the female makes a hole by which she enters. Soon after this the hole is completely shut again by a luxuriant excrescence from its margins, and so it remains until about a dozen workers have developed from the eggs of the female, when the hole is opened anew from within by these workers. It would appear that the female ants, living in cells closed all around, must be protected against any enemy; but notwithstanding a rather large number of them are devoured by the grub of a parasitic wasp belonging to the Chalcididæ; Mr. Westwood has observed that the pupæ of the Chalcididæ exhibit a much nearer approach to the obtected pupæ of the Lepidoptera than is made by any other Hymenoptera" ("Introd. to the Modern Classif. of Insects," Part XI., p. 162). Now the pupa of the parasite of the Imbauba ant is suspended on the wall of the cell by its posterior extremity just like the chrysalis of a butterfly.

I hope you will have received a paper on Æglea, a curious Decapod inhabiting the mountain rivulets of our Serra do Mar. Lately I obtained a large number of specimens of this Æglea, and among them a female with eggs in an advanced state of development. Thus I was enabled to satisfy myself that, like so many fresh-water and terrestrial animals, the marine allies of which undergo a transformation, our Æglea does not experience any metamorphosis.

FRITZ MÜLLER

Itajahy, St. Catharina, Brazil, Dec. 25, 1875