Observations on the membranous components of amphibian oocyte nucleoli.

Nucleoli in some large yolky oocytes of Plethodon cinerens and Ascaphus truei have attached to them a filament which may or may not have a beaded appearance. These filaments have been called ' nucleolar tails'. One nucleus may contain several hundred of them. They may be up to 200 /tm long and are usually about 1 /tm wide. The beads which are sometimes attached to the filament are round, refractile and up to 3 /*m in diameter. The tails are a feature of nuclei in which the nucleoli have left the nuclear envelope and migrated inward to cluster around the chromosomes in the centre of the nucleus. The tails project radially outwards from the central mass of nucleoli. Tails may be attached to round solid nucleoli, as is usually the case in A. truei, or they may be attached to ring nucleoli, as is often the case in P. cinereus, or they may lie free in the nuclear sap. Those nucleoli which remain attached to the nucleolar organizing site on the lampbrush chromosomes of P. cinereus never have tails. Nucleolar tails are Feulgen-negative and do not stain with gallocyanine when it is used under the proper conditions for staining nucleic acids. Tails are unaffected by deoxyribonuclease and ribonuclease but are destroyed by proteolytic enzymes.