n.

1. 【生】膜；壳；囊；鞘

n.

1. Anatomy  the loose sheath enclosing the spinal cord.
2. Anatomy  the outer layer of cells of a Graafian follicle.
3. Zoology  a cup-like or tubular structure containing a coral polyp.
4. Botany  each of the lobes of an anther, containing two pollen sacs.