Curtis Smyser, age 13, of Cheyenne, WY, for his question:
WHAT EXACTLY IS METAMORPHOSIS?
Metamorphosis is a Greek word that means "to transform." The word is used to describe the rather abrupt changes, or transformations, which occur in the form and structure of many lower animals from the time of their birth until they reach adulthood.
Many young animals, such as dogs and cats, look like their parents in form and structure. They differ chiefly in size from mature animals.
But when such insects as the butterfly or such invertebrates as the frog develop, they appear to be very different from the mature animals. In many of these young animals, striking changes in appearance and structure that is, metamorphosis must take place before they reach their adult condition.
A good example of metamorphosis can be seen in the life cycle of a butterfly. Because the butterfly passes through four separate stages of growth, scientists consider it an example of complete metamorphosis.
The first stage of the butterfly is an embryo that forms inside the egg.
When the future butterfly is newly hatched, it is known as a larva. In this stage it is a crawling, often fuzzy caterpillar. It may be brown, yellow or green. It may be smooth or hairy or have long spines.
In the larva stage, the creature eats a great deal and grows rapidly, molting or shedding its skin several times. After about a month in this stage, it enters its third period of existence, called the pupal stage.
The larva changes into an almost motionless, stiff object called a chrystalis. It usually hangs from a twig or from the underside of a leaf. Within the shell the larva changes into a pupa where the body, wings and legs of the mature insect develop.
Then the case splits open and the fully developed adult or imago emerges.
The pupal period may last from two weeks to many months. In the metamorphosis of a frog, the animal changes from an egg to a tadpole, and finally into the adult.
The grasshopper is an insect which also passes through three stages of development, omiting the pupal period found in the butterfly. Scientists call this metamorphosis incomplete.
In the frog's metamorphosis, the tadpole lives under water and breathes by means of gills. But as it grows larger, it develops lungs and pairs of forelegs and hind legs. Gradually, the tadpole loses its gills and tail by absorbing them into its body.
Chemical substances which the tadpole secretes from ductless glands bring about all these metamorphoses or changes. When the tadpole is ready to leave its home in the water and live mostly on land, the metamorphosis is finished.