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 Asphalax
and Proteus.
Birds of many kinds are extremely abundant on the undulating, grassy
plains around Maldonado. There are several species of a family allied
in structure and manners to our Starling: one of these (Molothrus
niger) is remarkable from its habits. Several may often be seen
standing together on the back of a cow or horse; and while perched on a
hedge, pluming themselves in the sun, they sometimes attempt to sing,
or rather to hiss; the noise being very peculiar, resembling that of
bubbles of air passing rapidly from a small orifice under water, so as
to produce an acute sound. According to Azara, this bird, like the
cuckoo, deposits its eggs in other birds' nests. I was several times
told by the country people that there certainly is some bird having
this habit; and my assistant in collecting, who is a very accurate
person, found a nest of the sparrow of this country (Zonotrichia
matutina), with one egg in it larger than the others, and of a
different colour and shape. In North America there is another species
of Molothrus (M. pecoris), which has a similar cuckoo-like habit, and
which is most closely allied in every respect to the species from the
Plata, even in such trifling peculiarities as standing on the backs of
cattle; it differs only in being a little smaller, and in its plumage
and eggs being of a slightly different shade of colour. This close
agreement in structure and habits, in representative species coming
from opposite quarters of a great continent, always strikes one as
interesting, though of common occurrence.
Mr. Swainson has well remarked, [8] that with the exception of the
Molothrus pecoris, to which must be added the M. niger, the cuckoos are
the only birds which can be called truly parasitical; namely, such as
"fasten themselves, as it were, on another living animal, whose animal
heat brings their young into life, whose food they live upon, and whose
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