2. Introduction
Metamorphosis is tranformation or change from
one form to another.
Metamorphosis is seen both in invertebrates and
chordates.
For example insects, echinoderms,amphibians,
fishes and so on.
3.
4. AMPHIBIANS
Amphibians is a class under chordates.
They are found almost everywhere.
These are the group of amphibians that show link
between aquatic and terrestrial mode of life.
Some charachterstic feature of amphibians are they are
cold blooded, have three chambered heart, 10 pairs of
cranial nerves, undergo indirect development.
5. Comparison between larval and adult
stage in Anurans
Larval Stage Adult Stage
Gills present, larval hb.
Herbivores, long digestive
tract, small mouth.
Nictitating membrane
absent, porphyropsin.
Largely ammonia.
Thin skin, no mucous
gland.
Gills absent, lungs well
developed, adult hb.
Carnivores, short digestive
tract, large mouth.
Nictitating membrane
present, rhodopsin.
Largely urea.
Thick skin, mucous glands.
6. Devlopment
Stages of growth can be roughly divided as:
1. Embryo
2. Larva
3. Adult
Stages of metamorphosis can be roughly divided into:
1. Prematamorphic period
2. Prometamorphic period
3. Metamorphic climax
7. Changes During Metamorphosis
Premetamorphic period in Rana pipiens last for 7 weeks.
It’s the growth period without much change in body
With emergence of hind limb starts the “Prometamorphic period”.
This period is marked with most of the changes and lead to
metamorphic climax.
The changes in prometamorphic change includes growth of hind
limbs, thinning of operculum, appearance of forelimbs, reposition of
eyes, shift in position of anus, mouth becomes wider, muscular jaws
develops, tail and gills are completely reabsorbed.
The rapid series of events following emergence of forelimbs to
achieve definite adult body are designated collectively as
metamorphic climax.
The most dramatic change during climax is reabsorption of tadpole
tail.
8.
9. Other Highlights Of Metamorphosis
These events are coordinated i.e. limbs develop first before
tail regresses.
Different tissues require different threshold dose of hormone
to undergo changes.
Main hormones playing role in metamorphosis is thyroxin,
prolactin.
Element influencing metamorphosis is Iodine.
Iodine has been seen to cause metamorphosis even in
thyroidectomized axolotl.
Metabolites available from tissue destruction are available for
other anabolic process.
Double metamorphosis.
Paedomorphosis.
some changes new other rudimentary and some same,Period may vary according to environmental conidition,size increase, hind limbs grow more than torso, in urodeles tail remains only tail fins are reabsorbed.
Gills disappears after complete of lung muscles, forelimb require greater dose to break through than hindlimbs and even more quantity is required for tail reabsorption., Paedomorphosis ambystoma, Necturus