The _paguro_ crab is born with the lower part of his case unprotected,--a most excellent tid-bit, tender and savory for hungry fishes.

The necessity for defending himself makes him seek a snail shell in order to protect the weak part of his organism.

If he encounters an empty dwelling of this class, he appropriates it.

If not, he eats the inhabitant, introducing his posterior armed with two hooked claws into its mother-of-pearl refuge.
But these defensive precautions are not sufficient for the weak _paguro_.

In order to live he needs rather to put himself on the offensive, to inspire respect in devouring monsters, especially in the octopi that are seeking as prey his trunk and hairy claws, exposed to locomotion outside his tower.
In course of time a sea-anemone comes along and attaches itself to the calcareous peak, the number often amounting to five or six, although there is no bodily relation between the _paguro_ and the organisms on top.