(_Tachyglossus aculeatus_)
No one who looked at the portrait of the spiny ant-eater for the
first time, and had no knowledge of its anatomy or history, would
be likely to guess that it was a near relative of the duckbill. But
in natural history, when we have to deal with members of different
groups, externals count for very little, and all depends upon internal
organisation. In the latter respect the echidnas, for there is more
than one species, resemble in all essential features the duckbill,
as they do in laying hard-shelled eggs, from which the young are
eventually hatched. The single egg of the echidna, in place of being
laid in a burrow, is, however, carried about by the female in a pouch
developed for the purpose on the under side of her body shortly before
the egg is laid; and in this same temporary pouch the young is likewise
nurtured during the earlier stages of its existence.
The duckbill and the echidna afford an excellent example of the
diversity of appearance produced in animals more or less nearly related
to each other by specialisation and adaptation to totally distinct
modes of life. In the duckbill the specialisation and adaptation are
for an aquatic existence; in the echidna they are for a burrowing,
terrestrial life and a diet of ants.
To an ant-eater teeth of any kind would be not only useless, but an
actual hindrance, and they have accordingly been discarded, while the
muzzle has been prolonged into a decidedly bird-like beak. In this
respect the echidna much resembles the great South American ant-eater,
which belongs to a totally different group of mammals.
To enable it to dig out the nests of the ants which form its chief
food, and likewise to excavate the burrows in which it passes the day,
the echidna is armed with powerful claws, those on the hind-feet being,
however, much larger and more curved than those in front. It is with
these strong hind-claws that the earth loosened by the fore-feet is
thrown out from ants’ nests and the burrow. Like the porcupine, which
is also a nocturnal and a burrowing creature, the echidna has its back
protected with an array of parti-coloured horny spines mingled with
hairs. The degree of development of the spines is, however, subject to
great variation; and there is one race in which the hair predominates,
and the spines appear only in the midst of the dense brown fur. Like
the platypus, the echidna has no external ears.
[Illustration]
The ordinary, or five-toed, echidna has a much more extensive range
than the platypus, occurring, in suitable localities, not only all
over Australia and Tasmania, but likewise in New Guinea. The last-named
island is likewise the home of the much larger three-toed echidna
(_Proechidna bruijnii_), in which the beak is longer, more slender, and
distinctly curved, while the number of the toes on each foot is reduced
to three.
With the commencement of evening the echidna issues forth from the lair
or burrow, in which it has passed the day, in search of food--this
comprising not only ants, both ordinary and white, but likewise such
other insects and their grubs as may be encountered or dug up during
the nocturnal wanderings. Soon after daybreak the creature returns to
its burrow. During the hottest and driest part of the Australian summer
spiny ant-eaters fall into a torpid condition, when they exist for
weeks at a time on no other nourishment but their own fat. In cases of
extreme hunger they are stated to fill their stomachs with sand. At
the end of the dry season, when rain falls and the country resumes its
verdure, the echidnas wake up, and the males relinquish their normally
solitary life and take to themselves partners.
On occasions of danger the echidna has two means of defence--it can
either roll itself up into a ball and present a sphere of spikes to its
enemy, or it can burrow with such rapidity that it actually seems to
sink into the earth as if swimming.
The single egg appears to be conveyed to the pouch by the female in her
mouth, and the parent assists the young echidna, whose muzzle is armed
with a special knob for that purpose, in breaking the shell. Naked and
blind when first hatched, the young one remains in the pouch till its
spines make their appearance, drawing its nutriment from two pores
through which the milk flows. When the young echidna has been turned
adrift in the world to shift for itself, the maternal breeding-pouch
shrivels up, to be re-developed the following year.
As in the case of the platypus, no remains of extinct echidnas are
found anywhere except in the superficial deposits of Australia itself.
Certain teeth from rocks older than the Chalk, both in Europe and
America, may, however, indicate the ancestral stock of the egg-laying
group.