38 MALDONADO, (CHAP. m. 



with him) oft the gradually-a^z>^ blindness of the Aspalax, a 

 Gnawer living under 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. 



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, re- 

 sembling 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,* 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 death would cause theirs during the period of infancy." It is 

 remarkable that some of the species, but not all, both of the Cuckoo 

 and Molothrus, should agree in this one strange habit of their parasitical 

 propagation, whilst opposed to each other in almost every other habit : 

 Ihe molothrus, like our starling, is eminently sociable, and lives on the 

 3pen plains without art or disguise : the cuckoo, as every one knows, 

 8 a singularly shy bird; it frequents the most retired thickets, and 

 * Magazine of Zoology and Botany, vol. i., p. 217. 



