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A tadpole or polliwog (also pollywog, polliwig, polewig, or polwig) is the wholly aquatic larval stage in the life cycle of an amphibian
Amphibian

Amphibians , such as frogs, toads, salamanders, newts and caecilians, are cold-blooded animals that metamorphose from a juvenile, water-breathing form to an adult, air-breathing form....
.

ng the tadpole stage of the amphibian life cycle, most respire by means of autonomous external or internal gill
Gill

A gill is an anatomical structure found in many aquatic ecosystem organisms. It is a respiration organ whose function is the extraction of oxygen from water and the excretion of carbon dioxide....
s. They do not usually have arms or legs until the transition to adulthood, and typically have dorsal or fin-like appendages and a tail with which they swim by lateral undulation
Lateral undulation

Lateral undulation is the most primitive of vertebrate locomotor patterns, present even in hagfish, lampreys, and lancelets. It is used both in the water and on land, most notably by snakes in the latter setting....
, similar to most fishes.

As tadpoles mature, they most commonly metamorphosize
Metamorphosis

.Metamorphosis is a biological process by which an animal physically developmental biology after birth or hatching, involving a conspicuous and relatively abrupt change in the animal's form or structure through cell cell growth#Cell reproduction and cell differentiation....
 by gradually growing limbs and then (most commonly in the case of frogs) outwardly absorbing its tail by apoptosis
Apoptosis

Apoptosis is the process of programmed cell death that may occur in multicellular organisms. Programmed Cell death involves a series of biochemical events leading to a characteristic cell Morphology and death, in more specific terms, a series of biochemical events that lead to a variety of morphological changes, including Bleb , changes...
.






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A tadpole or polliwog (also pollywog, polliwig, polewig, or polwig) is the wholly aquatic larval stage in the life cycle of an amphibian
Amphibian

Amphibians , such as frogs, toads, salamanders, newts and caecilians, are cold-blooded animals that metamorphose from a juvenile, water-breathing form to an adult, air-breathing form....
.

General description

During the tadpole stage of the amphibian life cycle, most respire by means of autonomous external or internal gill
Gill

A gill is an anatomical structure found in many aquatic ecosystem organisms. It is a respiration organ whose function is the extraction of oxygen from water and the excretion of carbon dioxide....
s. They do not usually have arms or legs until the transition to adulthood, and typically have dorsal or fin-like appendages and a tail with which they swim by lateral undulation
Lateral undulation

Lateral undulation is the most primitive of vertebrate locomotor patterns, present even in hagfish, lampreys, and lancelets. It is used both in the water and on land, most notably by snakes in the latter setting....
, similar to most fishes.

As tadpoles mature, they most commonly metamorphosize
Metamorphosis

.Metamorphosis is a biological process by which an animal physically developmental biology after birth or hatching, involving a conspicuous and relatively abrupt change in the animal's form or structure through cell cell growth#Cell reproduction and cell differentiation....
 by gradually growing limbs and then (most commonly in the case of frogs) outwardly absorbing its tail by apoptosis
Apoptosis

Apoptosis is the process of programmed cell death that may occur in multicellular organisms. Programmed Cell death involves a series of biochemical events leading to a characteristic cell Morphology and death, in more specific terms, a series of biochemical events that lead to a variety of morphological changes, including Bleb , changes...
. Lungs develop around the time of leg development and tadpoles late in development will often be found near the surface of the water where they breathe air. During the final stages of external metamorphosis, the tadpole's mouth changes from a small enclosed mouth at the front of the head to a large mouth the same width as the head. The intestines shorten to make way for the new diet. Most tadpoles are herbivorous, subsisting on algae and plants. Some species are omnivorous, eating detritus
Detritus

Detritus is a biological term used to describe dead or waste organic material.Detritus may also refer to:* Detritus , a geological term used to describe the particles of rock produced by weathering...
 and, whenever available, other tadpoles.

An exception to the rule distinct differences between the tadpole (juvenile) and adult (frog, toad, salamander etc) stages is the axolotl
Axolotl

The axolotl , Ambystoma mexicanum, is the best known of the Mexican neoteny mole salamanders belonging to the Tiger Salamander complex....
. Axolotls exhibit a property called neoteny
Neoteny

Neoteny , also called juvenilization, is the retention, by adults in a species, of traits previously seen only in juveniles , and is a subject studied in the field of developmental biology....
, meaning that they reach sexual maturity
Sexual maturity

Sexual maturity is the age or stage when an organism can sexual reproduction. It is sometimes considered synonymous with adulthood, though the two are distinct....
 without undergoing metamorphosis.

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