Strange mammals that lay eggs
1.
Platypus
Platypus has little-tiny eyes, a flat head and silky-smooth
looking short hair. It belongs to the great class of mammals, the furry or hairy
animals. These strange mammals that do
not give birth to young, but lay eggs! All animals (or almost all) begin life
the same way, as an egg-cell formed by the union of cells from two parents.
This egg-cell may develop in the mother's body, nourished and protected by her,
as in most mammals, or it may be made up into a package with all the food
material it will need to develop and pass out of the mother's body as an egg.
In this case it is hatched by the heat of the sun or kept warm by the mother.
Some members of egg-laying classes, many sharks and some snakes, retain their
eggs inside the mother's body until the young hatch and are born.
Of all the mammals living in this world today, only those of one
order, the Monotremata (found in Australia, Tasmania and New Guinea), lay eggs.
When this fact of egg-laying mammals was first reported, it was not believed by
the scientists. So many strange tales turned out to be false that it is best to
accept stories only after careful study of the evidence.
In 1884, however, a scientist named Caldwell went to Australia
from England, especially to gather full and reliable information about the
duckbill and echidna, or spiny ant eater, two types that belong in this strange
order. He discovered beyond shadow of doubt that both really do lay eggs and
after the eggs have hatched, the mother feeds her babies with milk, as other
mammal mothers do.
Platypus is a delicate animal and very hard to keep in captivity
out of its natural surroundings. However, a number of duckbills have been kept
alive and watched carefully by many people.
These animals lay eggs and after the eggs hatch, nourish the young
with milk. They are of two distinct kinds: the velvet-coated duckbill, or
platypus; and the spiny an eater or echidna.
When the first stuffed specimens of the duckbill, or platypus,
were brought to Europe they were thought to be frauds, like the "mermaids,"
Velvety fur like a mole: short, flattened tail like that of a
beaver, all four feet webbed; a bill like a duck and no teeth – no wonder
people found the duckbill hard to believe!
And when the collectors reported that the Australian men said this
astonishing creature laid eggs like a lizard or turtle, that was going too far!
The scientific names the duck bill was given indicate how people
felt-it was first called Platypus, or duck-like flat-foot," and then
Ornithorhynchus paradoxus, which means puzzling bird-snout." And a curious
puzzle he is.
Duckbills feed on snails, crayfish, earth-worms, water-living insects
and insect larvae. Most of this food they capture by probing about in the mud
at the bottom of the ponds in which they live. To assist in keeping the food
caught under water, there are large cheek pouches, in which the prey may be
stored. Duckbills can remain under water for six or seven minutes at a time.
Duckbills are found only in southern and eastern Australia and in
Tasmania, where they live in the small rivers, streams and ponds. They cannot
build dams as the beaver does, so they have to choose water that never goes
dry. Even in places where they are common, duckbills are not often seen, for
they come out of their burrows only rarely during the daylight hours. They are
shy animals, especially the old males.
The duckbill is a thick, heavy-bodied mammal; the males reach more
than twenty inches in length and may weigh nearly four pounds, while the
females are several inches shorter and a pound lighter in weight. In color
platypuses are deep, rich brown above, grayish or white below. The limbs are
short. Unlike those of most mammals, the upper arm and thigh project at right angles to the body, parallel to the
ground, like the limbs of a reptile. The feet have broad webs which aid in swimming.
The webs of the forefeet are especially large, extending far beyond the claws.
Duck bills, at home in the water, swim very well indeed, but walk on land
clumsily. Males have a long, sharp, horny spur on the heel; this spur is hollow
and connects with poison glands in the leg. The duck like bill is covered with
blackish, naked skin and, although the young platypus has several teeth, these
are lost before the animal becomes adult. In their place are developed horny
plates or ridges on the jaws and across the palate. The eyes are small and bright, while the
external ear is only a hole. No ear-shell, such as mammalian ears usually have,
is developed in duck bills. If one is alarmed it makes a warning
"splash-plunge" in the water and all other duckbills hearing the
noise sink below the surface and swim to their burrows or to some distance from
the threatened danger.
The home burrows are quite ambitious projects. A long tunnel is
dug into the bank of a pond or stream from below the water level, sloping
gently upward. This tunnel may extend for as much as fifty feet. It ends in a
rounded chamber. Sometimes several tunnels are dug to other chambers,
and the entrance to one of the tunnels is usually on the bank
above the water, hidden among bushes or by grass.
The duckbill is an expert digger, even though the webs on the
forefeet project beyond the claws. There is a beautiful adaptation here, for
the web folds back like a small umbrella into the palm, leaving the sharp claws
exposed and ready for the work of digging.
The home of the platypus is a burrow dug far into the bank of a
stream, from under the water. There is a very long, upward sloping tunnel,
which leads to the "living-room." Here is a bed of moist leaves and the
water plants, in which the mother lays her eggs. While the young are in this
nest, their mother blocks the entrance with a ball of leaves and earth, so no
other animal can enter. Even the father platypus does not enter the home during
this period. When the babies are a little older, the ball is broken up and
pushed aside, to leave the entrance clear. The duckbills, as they are also
called, are very shy, and swim away, or to their burrows, at any warning of
danger.
Fig. The burrow of Platypus
Despite their large quantity, little is
known about the life cycle of the platypus in the wild, and few of them have
been kept successfully in captivity. The sexes avoid each other except to mate,
and they do not mate until they are at least four years old. Males often fight
during the breeding season, inflicting wounds on each other with their sharp
ankle spurs. Courtship and mating take place in the
water from late winter through spring. Mating is a laborious affair; in one
recorded session the male was seen tightly grasping the tail of the female with
his bill as she led him on an exhaustive chase.
Duckbill
eggs are about the size of sparrow eggs and have thin, flexible shells, like
the skin on the inside
of a hen’s egg, but tougher. The nest material is kept damp, which makes certain
that the eggs will be kept moist, for otherwise they might easily dry up. Pregnancy is
at least two weeks (possibly up to a month), and incubation of the eggs takes
perhaps another 6 to 10 days. The eggs hatch after being incubated for a week
to ten days. The young ones are very small at first, naked and with a short, fleshy
beak. Baby duckbills do not for the first few days; then they begin e nourished
by the mother's milk. There are no nipples, but the babies suck milk from the special
mammary hairs and remain protected in the burrow, suckling for
three to four months before becoming independent. Hatchlings, whose weight
often increases by a factor of 20 during their first 14 weeks of life, possess
vestigial teeth that are shed shortly after the young platypus leaves the
burrow to feed on its own. Males take no part in rearing
the young. Females construct specially built nursery burrows, where
they usually lay two small leathery eggs.
The female incubates the eggs by curling around them with her tail touching her
bill.
