minutus or _pichy_, the D. villosus or _peludo_, and the _apar_. The
first extends ten degrees further south than any other kind; a fourth
species, the _Mulita_, does not come as far south as Bahia Blanca. The
four species have nearly similar habits; the _peludo_, however, is
nocturnal, while the others wander by day over the open plains, feeding
on beetles, larvae, roots, and even small snakes. The _apar_, commonly
called _mataco_, is remarkable by having only three moveable bands; the
rest of its tesselated covering being nearly inflexible. It has the
power of rolling itself into a perfect sphere, like one kind of English
woodlouse. In this state it is safe from the attack of dogs; for the
dog not being able to take the whole in its mouth, tries to bite one
side, and the ball slips away. The smooth hard covering of the
_mataco_ offers a better defence than the sharp spines of the hedgehog.
The _pichy_ prefers a very dry soil; and the sand-dunes near the coast,
where for many months it can never taste water, is its favourite
resort: it often tries to escape notice, by squatting close to the
ground. In the course of a day's ride, near Bahia Blanca, several were
generally met with. The instant one was perceived, it was necessary,
in order to catch it, almost to tumble off one's horse; for in soft
soil the animal burrowed so quickly, that its hinder quarters would
almost disappear before one could alight. It seems almost a pity to
kill such nice little animals, for as a Gaucho said, while sharpening
his knife on the back of one, "Son tan mansos" (they are so quiet).
Of reptiles there are many kinds: one snake (a Trigonocephalus, or
Cophias [18]), from the size of the poison channel in its fangs, must
be very deadly. Cuvier, in opposition to some other naturalists, makes
this a sub-genus of the rattlesnake, and intermediate between it and
the viper. In confirmation of this opinion, I observed a fact, which
appears to me very curious and instructive, as showing how every
character, even though it may be in some degree independent of
structure, has a tendency to vary by slow degrees. The extremity of the
tail of this snake is terminated by a point, which is very slightly
enlarged; and as the animal glides along, it constantly vibrates the
last inch; and this part striking against the dry grass and brushwood,
produces a rattling noise, which can be distinctly heard at the
distance of six feet. As often as the animal was irritated or
surprised, its tail was shaken; and the vibrations were extremely
rapid. Even as long as the body retained its irritability, a tendency
to this habitual movement was evident. This Trigonocephalus has,
90