External Protective Covering

External protective covering crossword clue, 11 letters. A quick clue found in Daily Telegraph Friday 27 Oct 2017.

The answer: EXOSKELETON

External protective covering crossword clue

Whereas most mammals maintain a protected internal environment for the growing fetus, birds use an external protective covering consisting of calcium called a “shell.” This protective shell provides an isolated environment to allow the developing chick to thrive but once the chick is ready to survive in the outside world, this secure vault needs to be opened. The chick needs to break open the shell without help, in its own time frame and only the chick’s internal clock knows when it is time to emerge.