of the two known kinds of fish in which the female shows a sense of
her position as a mother. The tube-mouth, as you can see at a glance,
is a close relation of our old friend the seahorse, whose disguised
and undisguised forms in Australia and the Mediterranean we have
already observed when dealing with the question of animal
masqueraders. Solenostoma is a native of the Indian Ocean, from
Zanzibar to China. In the male, the lower pair of fins are separate,
as is usual among fish; but in the female, represented in the
accompanying sketch, they are lightly joined at the edge, so as to
form a sort of pouch like a kangaroo's, in which the eggs are
deposited after being laid, and thus carried about in the mother's
safe keeping. No. 5 shows the arrangement of this pouch in detail,
with the eggs inside it. The mother Solenostoma not only takes charge
of the spawn while it is hatching in this receptacle, but also looks
after the young fry, like the father stickleback, till they are of an
age to go off on their own account in quest of adventures. The most
frequent adventure that happens to them on the way is, of course,
being eaten.
[Illustration: NO. 5. POUCH OF TUBE-MOUTH.]
[Illustration: NO. 6. PIPE-FISH.]
The common English pipe-fish is a good example of the other and much
more usual case in which the father alone is actuated by a proper
sense of parental responsibility. The pipe-fish, indeed, might almost
be described as a pure and blameless rate-payer. No. 6 shows you the
outer form of this familiar creature, whom you will recognize at a
glance as still more nearly allied to the sea-horses than even the
tube-mouth. Pipe-fishes are timid and skulking creatures. Like their
horse-headed relations, they lurk for the most part among sea-weed
for protection, and being but poor swimmers, never venture far from
the covering shelter of their native thicket. But the curious part of
them is that in this family the father fish is provided with a pouch
even more perfect than that of the female tube-mouth, and that he
himself, not his mate takes sole charge of the young, incubates them
in his sack, and escorts them about for some time after hatching. The
pouch, which is more fully represented in No. 7, is formed by a loose
fold of skin arising from either side of the creature. In the
illustration this fold is partly withdrawn, so as to show the young
pipe-fish within their safe retreat after hatching out. It is said, I
know not how truly, that the young fry will stroll out for an
occasional swim on their own account, but will return at any threat of
danger to their father's bosom, for a considerable time after the
first hatching. This is just like what one knows of kangaroos and many
other pouched mammals, where the mother's pouch becomes a sort of
nursery, or place of refuge, to which the little ones return for
warmth or safety after every excursion.
[Illustration: NO. 7. POUCH OF PIPE-FISH.]
The sea-horses and many other fish have similar pouches; but, oddly
enough, in every case it is the male fish which bears it, and which
undertakes the arduous duty of nurse for his infant offspring.
A few female fish, on the other hand, even hatch the eggs within their
own bodies, and so apparently bring forth their young alive, like the
English lizard among reptiles. This, however, is far from a common
case: indeed, in an immense number of instances, neither parent pays
the slightest attention to the eggs after they are once laid and got
rid of: the spawn is left to lie on the bottom and be eaten or spared
as chance directs, while the young fry have to take care of
themselves, without the aid of parental advice and education. But
exceptions occur where both parents show signs of realizing the
responsibilities of their position. In some little South American
river fish, for instance, the father and mother together build a nest
of dead leaves for the spawn, and watch over it in unison until the
young are hatched. This case is exactly analogous to that of the doves
among birds: I may add that wherever such instances occur they always
seem to be accompanied by a markedly gentle and affectionate nature.
Brilliantly-coloured fighting polygamous fishes are fierce and cruel:
monogamous and faithful animals are seldom bright-hued, but they mate
for life and are usually remarkable for their domestic felicity. The
doves and love-birds are familiar instances.
Frogs are very closely allied to fish: indeed, one may almost say that
every frog begins life as a fish, limbless, gill-bearing, and aquatic,
and ends it as something very like a reptile, four-legged,
lung-bearing, and more or less terrestrial. For the tadpole is
practically in all essentials a fish. It is not odd, therefore, to
find that certain frogs reproduce, in a very marked manner, the
fatherly traits of their fish-like ancestors. There is a common kind
of frog in France, Belgium, and Switzerland, which does not extend to
England, but which closely recalls the habits of the stickleback and
the pipe-fish. Among these eminently moral amphibians, it is the
father, not the mother, who takes entire charge of the family. The
female lays her spawn in the shape of long strings or rolls, looking
at first sight like slimy necklaces. I have seen them as much as a
couple of yards long, lying loose on the grass where the frog lays
them. As soon as she has deposited them, however, the father frog hops
up, twists the garlands dexterously in loose festoons round his legs
and thighs, and then retires with his precious burden to some hole in
the bank of his native pond, where he lurks in seclusion till the eggs
develop. Frogs do not need frequent doses of food--their meals are
often few and far between--and during the six or eight weeks that the
eggs take to mature the father probably eats very little, though he
may possibly sally forth at night, unobserved, in search of provender.
At the end of that time the devoted parent, foreseeing developments,
takes to the water once more, so that the tadpoles may be hatched in
their proper element. I may add that this frog is a great musician in
the breeding season, but that as soon as the tadpoles are hatched out
he loses his voice entirely, and does not recover his manly croak till
the succeeding spring. This is also the case with the song of many
birds, the crest of the newt, the plumes of certain highly-decorated
trogons and nightjars, and, roughly speaking, the decorative and
attractive features of the male sex in general. Such features are
given them during the mating period as allurements for their
consorts: they disappear, for the time at least, like a ball-dress
after a ball, as soon as no immediate use can any longer be made of
them.
[Illustration: POUCHED FROG.]
Some American tree-frogs, on the other hand, imitate rather the
motherly Solenostoma than the fatherly instincts of the pipe-fish or
the stickleback. These pretty little creatures have a pouch like the
kangaroo, but in their case (as in the kangaroo's) it is the female
who bears it. Within this safe receptacle the eggs are placed by the
male, who pushes them in with his hind feet; and they not only undergo
their hatching in the pouch, but also pass through their whole tadpole
development in the same place. Owing to the care which is thus
extended to the eggs and young, these advanced tree-frogs are enabled
to lay only about a dozen to fifteen eggs at a time, instead of the
countless hundreds often produced by many of their relations.
Tree-frogs have, of course, in most circumstances much greater
difficulty in getting at water than pond-frogs; and this is especially
true in certain tropical or desert districts. Hence most of the frogs
which inhabit such regions have had to find out or invent some
ingenious plan for passing through the tadpole stage with a minimum of
moisture. The devices they have hit upon are very curious. Some of
them make use of the little pools collected at the bases of huge
tropical leaf-stalks, like those of the banana plant; others dispense
with the aid of water altogether, and glue their new-laid eggs to
their own backs, where the fry pass through the tadpole stage with the
slimy mucus which surrounds them. Nature always discovers such cunning
schemes to get over apparent difficulties in her way: and the
tree-frogs have solved the problem for themselves in half a dozen
manners in different localities. Oddest of all, perhaps, is the dodge
invented by "Darwin's frog," a Chilean species, in which the male
swallows the eggs as soon as laid, and gulps them into the
throat-pouch beneath his capacious neck: there they hatch out and pass
through their tadpole stage: and when at last they arrive at frogly
maturity, they escape into the world through the mouth of their
father.
[Illustration: NO. 8. THE SURINAM TOAD.]
The Surinam toad, represented in No. 8, is also the possessor of one
of the strangest nurseries known to science. It lives in the dense
tropical forests of Guiana and Brazil, and is a true water-haunter.
But at the breeding season the female undergoes a curious change of
integument. The skin on her back grows pulpy, soft, and jelly-like.
She lays her eggs in the water: but as soon as she has laid them, her
lord and master plasters them on to her impressionable back with his
feet, so as to secure them from all assaults of enemies. Every egg is
pressed separately into a bed of the soft skin, which soon closes over
it automatically, thus burying each in a little cell or niche, where
it undergoes its further development. The tadpoles pass through their
larval stage within the cell, and then hop out, in the four-legged
condition. As soon as they have gone off to shift for themselves, the
mother toad finds herself with a ragged and honeycombed skin, which
must be very uncomfortable. So she rubs the remnant of it off against
stones or the bark of trees, and re-develops a similar back afresh at
the next breeding season.
Almost never do we find a device in nature which occurs once only. The
unique hardly exists: nature is a great copyist. At least two animals
of wholly unlike kinds are all but sure to hit independently upon the
self-same mechanism. So it is not surprising to learn that a cat-fish
has invented an exactly similar mode of carrying its young to that
adopted by the Surinam toad: only, here it is on the under surface,
not the upper one, that the spawn is plastered. The eggs of this
cat-fish, whose scientific name is Aspredo, are pressed into the skin
below the body, and so borne about by the mother till they hatch. This
is the second instance of which I spoke above, where the female fish
herself assumes the care of her offspring, instead of leaving it
entirely to her excellent partner.
Higher up in the scale of life we get many instances which show
various stages in the same progressive development towards greater
care for the safety and education of the young. Among the larger
lizards, for example, a distinct advance may be traced between the
comparatively uncivilized American alligator and his near ally, the
much more cultivated African crocodile. On the banks of the
Mississippi, the alligator lays a hundred eggs or thereabouts, which
she deposits in a nest near the water's edge, and then covers them up
with leaves and other decaying vegetable matter. The fermentation of
these leaves produces heat and so does for the alligator's eggs what
sitting does for those of hens and other birds: the mother deputes her
maternal functions, so to speak, to a festering heap of decomposing
plant-refuse. Nevertheless, she loiters about all the time, like
Miriam round the ark which contained Moses, to see what happens; and
when the eggs hatch out, she leads her little ones down to the river,
and there makes alligators of them. This is a simple and relatively
low stage in the nursery arrangements of the big lizards.
The African crocodile, on the other hand, goes a stage higher. It lays
only about thirty eggs, but these it buries in warm sand, and then
lies on top of them at night, both to protect them from attack and to
keep them warm during the cooler hours. In short, it sits upon them.
When the young crocodiles within the eggs are ready to hatch, they
utter an acute cry. The mother then digs down to the eggs, and lays
them freely on the surface, so that the little reptiles may have space
to work their way out unimpeded. This they do by biting at the shell
with a specially developed tooth; at the end of two hours' nibbling
they are free, and are led down to the water by their affectionate
parent. In these two cases we see the beginnings of the instinct of
hatching, which in birds, the next in order in the scale of being, has
become almost universal.
I say _almost_ universal, because even among birds there are a few
kinds which have not to this day progressed beyond the alligator
level. Australia is the happy hunting-ground of the zooelogist in
search of antiquated forms, elsewhere extinct, and several Australian
birds, such as the brush-turkeys, still treat their eggs essentially
on the alligator method. The cock birds heap up huge mounds of earth
and decaying vegetable matter, as much as would represent several
cartloads of mould; and in this natural hot-bed the hens lay their
eggs, burying each separately with a good stock of leaves around it.
The heat of the sun and the fermenting mould hatch them out between
them; to expedite the process, the birds uncover the eggs during the
warmer part of the day, expose them to the sun, and bury them again in
the hot-beds towards evening. Several intermediate steps may also be
found between this early stage of communal nesting by proxy and the
true hatching instinct; a good one is supplied by the ostrich, which
partially buries its eggs in hot sand, but sits on them at intervals,
both father and mother birds taking shares by turn in the duties of
incubation.
The vast subject which I have thus lightly skimmed is not without
interest, again, from its human implications. Savages as a rule
produce enormous families; but then, the infant mortality in savage
tribes is proportionally great. Among civilized races, families are
smaller, and deaths in infancy are far less numerous. The higher the
class or the natural grade of a stock, the larger as a rule the
proportion of children safely reared to the adult age. The goal
towards which humanity is slowly moving would thus seem to be one
where families in most cases will be relatively small--perhaps not
more on an average than three to a household--but where most or all of
the children brought into the world will be safely reared to full
maturity. This is already becoming the rule in certain favored ranks
of European society.
[Illustration: TADPOLES AND YOUNG FROG.]
HOW ANIMALS SPEND THE WINTER
(FROM GLEANINGS FROM NATURE.)[2]
BY W. S. BLATCHLEY.
[2] "Popular Science Monthly," February, 1897. Copyright by William
Stanley Blatchley, 1899.
[Illustration: A COCOON.]
One of the greatest problems which each of the living forms about us
has had to solve, during the years of its existence on earth, is how
best to perpetuate its kind during that cold season which once each
year, in our temperate zone, is bound to come. Many are the solutions
to this problem. Each form of life has, as it were, solved it best to
suit its own peculiar case, and to the earnest student of Nature there
is nothing more interesting than to pry into these solutions and note
how varied, strange, and wonderful they are.
To fully appreciate some of the facts mentioned below it must be borne
in mind that there is no such thing as "spontaneous generation" of
life. Every cell is the offspring of a pre-existing cell. Nothing but
a living thing can produce a living thing. Hence every weed that next
season will spring up and provoke the farmer's ire, and every insect
which will then make life almost intolerable for man or beast, exists
throughout the winter in some form....
Beginning with the earth-worms and their kindred, we find that at the
approach of winter they burrow deep down where the icy breath of the
frost never reaches, and there they live, during the cold season, a
life of comparative quiet. That they are exceedingly sensitive to
warmth, however, may be proven by the fact that when a warm rain comes
some night in February or March, thawing out the crust of the earth,
the next morning reveals in our dooryards the mouths of hundreds of
the pits or burrows of these primitive tillers of the soil, each
surrounded by a little pile of pellets, the castings of the active
artisans of the pits during the night before.
If we will get up before dawn on such a morning we can find the worms
crawling actively about over the surface of the ground, but when the
first signs of day appear they seek once more their protective
burrows, and only an occasional belated individual serves as a
breakfast for the early birds.
The eyes of these lowly creatures are not visible, and consist of
single special cells scattered among the epidermal cells of the skin,
and connected by means of a sensory nerve fibre with a little bunch of
nervous matter in the body. Such a simple visual apparatus serves them
only in distinguishing light from darkness, but this to them is most
important knowledge, as it enables them to avoid the surface of the
earth by day, when their worst enemies, the birds, are in active
search for them.
The fresh-water mussels and snails and the crayfish burrow deep into
the mud and silt at the bottom of ponds and streams where they lie
motionless during the winter. The land snails, in late autumn, crawl
beneath logs, and, burrowing deep into the soft mould, they withdraw
far into their shells. Then each one forms with a mucous secretion two
thin transparent membranes, one across the opening of the shell and
one a little farther within, thus making the interior of the shell
perfectly air-tight. There for five or six months he sleeps, free from
the pangs of hunger and the blasts of winter, and when the balmy
breezes of spring blow up from the south he breaks down and devours
the protecting membrane and goes forth with his home on his back to
seek fresh leaves for food and to find for himself a mate.
Next in the scale come the insects, which comprise four-fifths of all
existing animals, and each one of the mighty horde seen in summer has
passed the winter in some form. One must look for them in strange
places and under many disguises; for they cannot migrate, as do the
majority of the birds, nor can they live an active life while the
source of their food supply, the plants, are inactive.
The majority of those insects which in May or June will be found
feeding on the buds or leaves of our trees, or crawling worm-like over
the grass of our lawns, or burrowing beneath the roots of our garden
plants, are represented in the winter by the eggs alone. These eggs
are deposited in autumn by the mother insect, on or near the object
destined to furnish the young, or larvae, their food. Each egg
corresponds to a seed of one of our annual plants; being, like it,
but a form of life so fashioned and fitted as to withstand for a long
period intense cold; the mother insect, like the summer form of the
plant, succumbing to the first severe frost.
Thus myriads of the eggs of grasshoppers are in the early autumn
deposited in the ground, in compact masses of forty to sixty each.
About mid-April they begin to hatch, and the sprightly little insects,
devoid of wings, but otherwise like their parents, begin their
life-work of changing grass into flesh.
[Illustration: HEDGEHOG CATERPILLAR.]
A comparatively small number of insects pass the winter in the larval
or active stage of the young. Of these, perhaps the best known is the
brown "woolly worm" or "hedgehog caterpillar," as it is familiarly
called. It is thickly covered with stiff black hairs on each end, and
with reddish hairs on the middle of the body. These hairs appear to be
evenly and closely shorn, so as to give the animal a velvety look; and
as they have a certain degree of elasticity, and the caterpillar curls
up at the slightest touch, it generally manages to slip away when
taken into the hand. Beneath loose bark, boards, rails, and stones,
this caterpillar may be found in mid-winter, coiled up and apparently
lifeless. On the first bright, sunny days of spring it may be seen
crawling rapidly over the ground, seeking the earnest vegetation which
will furnish it a literal "breakfast." In April or May the chrysalis,
surrounded by a loose cocoon formed of the hairs of the body
interwoven with coarse silk, may be found in situations similar to
those in which the larva passed the winter. From this, the perfect
insect, the Isabella tiger moth, _Pyrrharctia isabella_ Smith, emerges
about the last of June. It is a medium sized moth, dull orange in
color, with three rows of small black spots on the body, and some
scattered spots of the same color on the wings.
By breaking open rotten logs one can find in mid-winter the grubs or
larvae of many of the wood-boring beetles, and, beneath logs and stones
near the margins of ponds and brooks, hordes of the maggots or larvae
of certain kinds of flies may often be found huddled together in great
masses. The larvae of a few butterflies also live over winter beneath
chips or bunches of leaves near the roots of their food plant, or in
webs of their own construction, which are woven on the stems close to
the buds, whose expanding leaves will furnish them their first meal in
spring.
Many insects pass the winter in the quiescent or pupal stage; a state
exceedingly well fitted for hibernating, requiring as it does, no
food, and giving plenty of time for the marvellous changes which are
then undergone. Some of these pupae are enclosed in dense silken
cocoons, which are bound to the twigs of the plants upon which the
larvae feed, and thus they swing securely in their silken hammocks
through all the storms of winter. Perhaps the most common of these is
that of the brown Cecropian moth, _Attacus cecropia_ L., the large
oval cocoon of which is a conspicuous object in the winter on the
twigs of our common shade and fruit trees. Many other pupae may be
found beneath logs or on the under side of bark, and usually have the
chrysalis surrounded by a thin covering of hairs, which are rather
loosely arranged. A number pass the cold season in the earth with no
protective covering whatever. Among these is a large brown chrysalis
with a long tongue case bent over so as to resemble the handle of a
jug. Every farm boy has ploughed or spaded it up in the spring, and is
it but the pupa of a large sphinx moth, _Protoparce celeus_ Hub., the
larva of which is the great green worm, with a "horn on its tail," so
common on tomato plants in the late summer.
[Illustration: CHRYSALIS OF TOMATO WORM.]
Each of the winter forms of insects above mentioned can withstand long
and severe cold weather--in fact, may be frozen solid for weeks and
retain life and vigor, both of which are shown when warm weather and
food appear again. Indeed, it is not an unusually cold winter, but one
of successive thawings and freezings, which is most destructive to
insect life. A mild winter encourages the growth of mould which
attacks the hibernating larvae and pupae as soon as, from excess of rain
or humidity, they become sickly; and it also permits the continued
activity of insectivorous mammals and birds. Thus, moles, shrews,
and field mice, instead of burying themselves deeply in the ground,
run about freely during an open winter and destroy enormous numbers
of pupae; while such birds as the woodpeckers, titmice, and chickadees
are constantly on the alert, and searching in every crevice and cranny
of fence and bark of tree for the hibernating larvae.