scles and ligaments, which enable it to
dilate the mouth sufficiently to swallow bodies much larger than itself.

The largest grow to a length of thirty feet and upwards; but boas
ordinarily do not attain more than twenty feet in length.

THE SPOTTED BOA.

The boa scytale, or spotted boa, is of a greyish colour, marked with
round spots, and scarcely inferior in size to the former.

THE RINGED BOA.

There is another species--the ringed boa, or boa cenchris--which, though
growing to a considerable size, does not attain that of the former
species.

A curious species (the boa canina) has a large head, shaped somewhat
like that of a dog; the general colour a bright Saxon-green, with
transverse white bars down the back. The sides are of a deeper green,
and the belly is white.

Wallace describes a small one only eleven feet in length, but as thick
as a man's thigh. It was secured by having a stick tightly tied round
the neck. It went about dragging its clog with it, sometimes opening
its mouth with a very suspicious yawn, and sometimes turning its tail up
into the air. Being put into a cage, and released from the stick, it
began to breathe most violently, the expirations sounding like
high-pressure steam escaping from a Great Western locomotive.

The boa, however, is not much dreaded in South America, as it seldom or
never attacks man; which the anaconda is said always to do, if it can
find him unprepared. Stories are told of desperate encounters between
travellers in the forests of the Amazon and pythons or boas. A French
traveller narrates how, on one occasion, the whole of his attendants
took to flight on seeing a huge python approaching,--with the exception
of a gallant native, who, attacking the monster vigorously with a long,
lithe pole, struck it a blow which paralysed its powers; when, the party
returning, it was easily killed.

THE RATTLESNAKE.

Venomous as is the bite of the rattlesnake, and abounding as it does in
all parts of the continent, it is less dreaded than many other serpents.
It is, in the first place, very sluggish in its habits; and it is
happily compelled to bear about it an instrument which gives notice of
its approach and intention of biting. The South American rattlesnake--
the Boaquira crotalus horridus--has the rattle placed at the end of the
tail. It consists of several dry, hard, bony processes, so shaped that
the tip of each upper bone runs within two of the bones below it.