__ Sheath, the Material Surrounding Nerves
Puzzle 17 of Patterns in Nature Pack
Question is: __ Sheath, the Material Surrounding Nerves
and the answer is: MYELIN
Word Meaning:
MYELIN — (neuroanatomy) A white, fatty material, composed of lipids and lipoproteins, that surrounds the axons of nerves.
Definitions from Wiktionary.