A Membrane or Sac That Encloses a Body Structure

This page is the CodyCross answer for the clue below from Top Secret, Group 2084, Puzzle 5 (Bug Detector).

Question is: A Membrane or Sac That Encloses a Body Structure

and the answer is: CAPSULE

Word Meaning:

CAPSULE — (physiology) A membranous envelope.

Definitions from Wiktionary.