Encyclopedia of Biology

metamorphosis with no pupa and with young imma-
ture forms looking similar to the adult minus wings.
See alsoINCOMPLETE METAMORPHOSIS.

metanephridium Excretory organ or tubule sur-

rounded by capillaries in invertebrates (e.g., annelid

worms) in which nephrostomes, the internal ciliated

218 metanephridium

DNA

mRNA transcription

Mature mRNA

mRNA

Transport to cytoplasm for

protein synthesis (translation)

Nucleus

tRNA

Cell membrane

Template for protein synthesis. Each set of three bases, called codons, specifies a certain protein in the sequence of amino acids that
comprise the protein. The sequence of a strand of mRNA is based on the sequence of a complementary strand of DNA.(Courtesy of
Darryl Leja, NHGRI, National Institutes of Health)