Download 1 Frogs are members of the zoological class called

Frogs are members of the zoological class called Amphibia.
Amphibians are cold-blooded vertebrate animals. They are different from reptiles
because they lack scales and generally return to water to breed.
They are one of three types of Amphibians. Anura also called Salientia, caudate and
caecilians.
Frogs are characterised by long hind legs, a short body, webbed feet, protruding eyes
and no tail. Most frogs have a land and water lifestyle, but move easily on land by
jumping or climbing. They normally lay their eggs in puddles, ponds or lakes; and their
tadpoles, have gills and develop in water. Adult frogs follow a carnivorous diet, mostly
of arthropods, annelids and gastropods. Frogs are most noticeable by their call, which
can be widely heard during the night or day, mainly in their mating season.
Frog
Fossil range: Triassic - Recent
White's Tree Frog (Litoria caerulea)
Scientific classification
Kingdom: Animalia
Phylum:
Chordata
Class:
Amphibia
Order:
Anura
Merrem, 1820
Distribution of frogs (in black)
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Flatty Dobies: adipose tissue.
Vena cava: blood vessel that carries the blood to the heart.
Testicle: male sex organ which produces spermatozoa.
Spermatic canal: tube that carries sperm.
Adrenal gland: small gland on top of the kidney.
Kidney: blood-purifying organ.
Small intestine: part of the digestive tract between the stomach and the large
intestine.
Dorsal aorta: dorsal blood vessel that carries the blood from the heart to other
organs.
Large intestine: part of the digestive tract between the small intestine and the cloaca.
Ereter: tube that carries the urine from the kidneys to the bladder.
Bladder: pocket in which urine collects.
Cloaca: orifice shared by the urinary, genital and intestinal tracts of a frog.
Uterus: female genital organ that holds the fertilized egg during its development.
Oviduct: passage through which the egg leaves the body of the frog.
Ovary: reproductive gland that produces ova.
Frogs are easy to tell apart from female and male frog is during the breeding season
which is between February and March. During this time the male develops dark pads on
his forelimbs called nuptial pads. Also during this time the skin of the female becomes
rough to the touch, so that it is easy for the male to identify a female. At other times
of the year it is more difficult. Generally males are slightly larger, and tend to have
longer digits on their forelimbs. Another difference is that the male croak and the
female don't.
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Once adult frogs reach maturity, they will assemble at a pond or stream to breed. Many
frogs return to the area they were born, often resulting in annual migrations involving
thousands of frogs.
Male and female Common toad (Bufo bufo) in amplexus
Once at the breeding ground, male frogs call to attract a mate, a chorus of frogs. The
call is unique to the frogs, and will attract females of that species. Some species have
males who do not call, but intercept females that are approaching a calling male.
The male and female frogs then undergo amplexus. This involves the male mounting the
female and gripping her tightly. Fertilization is external. The female releases her eggs,
which the male frog covers with a sperm solution. The eggs then swell and develop a
protective coating. The eggs are brown or black, with a clear, gelatin-like covering.
Most temperate species of frogs reproduce between late autumn and early spring. Most
Reproducing in these conditions helps the developing tadpoles because dissolved oxygen
concentrations in the water are highest at cold temperatures. More importantly,
reproducing early in the season ensures that appropriate food is available to the
developing frogs at the right time.
Another way of frogs to mate
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Males arrive at the breeding pond first and begin a chorus of croaking. This attracts
the females. Once the females arrive the males jump onto the backs of the females and
cling on with their nuptial pads. This position is called amplexus. The female eventually
lays her eggs into the water. Simultaneously the male releases his sperm into the water
and on to the eggs in order to fertilise them. The fertilised eggs sink in the water and
the jelly coat swells as it takes in water to protect the embryos. The spawn then rises
to the top of the water.
Frog eggs are approximately 2-3mm in diameter, and a frog can lay about 2,000 eggs at
a time.
It is estimated that up to 20% of frogs
may care for their young in one way or
another, and there is a great diversity of parental behaviours.
Some species of poison dart frog lay eggs on the forest floor and protect them,
guarding the eggs from predation and keeping them moist. The frog will urinate on them
if they become too dry. After hatching, a parent will move them, on its back, to a
water-holding bromeliad. The parent then feeds them by laying unfertilized eggs in the
bromeliad until the young have metamorphosed. Other frogs carry the eggs and
tadpoles on their hind legs or back. Some frogs even protect their offspring inside
their own bodies. The male Australian Pouched Frog has pouches along its side in which
the tadpoles reside until metamorphosis. The female Gastric-brooding Frog swallows its
tadpoles, which then developes in the stomach. To do this, the Gastric-brooding Frog
must stop secreting stomach acid and suppress peristalsis (contractions of the
stomach). Darwin's Frog puts the tadpoles in its vocal sac for development.
Frogspawn turns into tadpoles after about 10 days and it takes another 12-14 weeks
before the tadpoles turn into froglets.
True Love
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When Frogs mate, the male frog clasps the female underneath in an embrace called
amplexus. He literally climbs on her back, reaches his arms around her "waist", either
just in front of the hind legs, just behind the front legs, or even around the head.
Amplexus can last several days! Usually, it occurs in the water. While in some cases,
complicated courting behavior occurs before mating, many species of frogs are known
for attempting to mate with anything that moves which isn't small enough to eat!
Spawn
While in the amplexus position, the male frog fertilizes the eggs as they get laid. Frogs
tend to lay eggs single eggs in masses, whereas toads usually lay eggs in long chains.
Some frogs leave after this point, but others stick around to watch over the little ones.
Some have very unusual ways of caring for their young.
Egg
Frogs tend to lay many eggs because there are many hazards between fertilisation.
Those eggs that die tend to turn white. The lucky ones that actually manage to hatch
still start out on a journey of many perils.
Life starts right as the central yolk splits in two. It then divides into four, then eight,
until it looks a bit like a raspberry inside a jelly cup. Soon, the embryo starts to look
more and more like a tadpole, getting longer and moving about in it's egg.
Usually it takes about 6-21 days after being fertilized, the egg will hatch. Most eggs
are found in calm waters, to prevent getting rumbled about in infancy.
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Tadpole
Shortly after hatching, the tadpole still feeds on the remaining yolk, which is actually in
its gut! The tadpole at this point consists of poorly developed gills, a mouth, and a tail.
It's really fragile at this point. They usually will stick themselves to floating weeds or
grasses in the water using little sticky organs between its' mouth and belly area. Then,
7 to 10 days after the tadpole has hatched, it will begin to swim around and feed on
algae.
After about 4 weeks, the gills start getting grown over by skin, until they eventually
disappear. The tadpoles get teeny tiny teeth which help them grate food turning it into
soupy oxygenated particles. They have long coiled guts that help them digest as much
nutrients from their meadger diets as possible.
By the fourth week, tadpoles can actually be fairly social creatures. Some even interact
and school like fish!
Tadpole with legs
After about 6 to 9 weeks, little tiny legs start to sprout. The head becomes more
distinct and the body elongates. By now the diet may grow to include larger items like
dead insects and even plants.
The arms will begin to bulge where they will eventually pop out, elbow first.
After about 9 weeks, the tadpole looks more like a teeny frog with a really long tail. It
is now well on it's way to being almost full grown.
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Young Frog, or Froglet
By 12 weeks, the tadpole has only a teeny tail stub and looks like a miniature version of
the adult frog. Soon, it will leave the water, only to return again to laymore eggs and
start the process all over again!
Frog
By between 12 to 16 weeks, depending on water and food supply, the frog has completed
the full growth cycle. Some frogs that live in higher altitudes or in colder places might
take a whole winter to go through the tadpole stage, others may have unique
development stages that vary from your "traditional" tadpole-in-the-water type life
cycle.
http://en.wikipedia.org/wiki/Frog#Life_cycle
Google images
http://allaboutfrogs.org/
http://allaboutfrogs.org/weird/weird.html
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