Nucleolus

• the somewhat spherical body within a nucleus; site of RNA synthesis
  Source: Noland, George B. 1983. General Biology, 11th Edition. St. Louis, MO. C. V. Mosby
• a nuclear body composed of rRNA and amplified copies of genes that code for rRNA
  Source: Jenkins, John B. 1990. Human Genetics, 2nd Edition. New York: Harper & Row
• The nucleolus is a region found within the cell nucleus that is concerned with producing and assembling the cell's ribosomes. Following assembly, ribosomes are transported to the cell cytoplasm where they serve as the sites for protein synthesis.