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 out as they are extended? Is the respiratory opening on the right or left side of the body? On the mantle fold or on the body? (Figs. 202-3-4.) How often does the aperture open and close?

a, mouth; b, b, foot; c. vent; d, d, lung; h, heart.

Blood vessels are black. (Perrier.)

Place the snail in a moist tumbler. Does the whole under surface seem to be used in creeping? Does the creeping surface change shape as the snail creeps? Do any folds or wrinkles seem to move either toward the front or rear of its body? Is enough mucus left to mark the path traveled? The fold moves to the front, adheres, and smooths out as the slug or snail is pulled forward.

Cephalopods.—The highest and best developed mollusks are the cephalopods, or "head-footed" mollusks. Surrounding the mouth are eight or ten appendages which serve both as feet and as arms. These appendages have two rows of sucking disks by which the animal attaches itself to the sea bottom, or seizes fish or other prey with a firm grip. The commonest examples are the squid, with a long body and ten arms, and the octopus, or devilfish, with a short body and eight arms. Cephalopods have strong biting mouth parts and complex eyes somewhat resembling the eyes of backboned, or vertebrate, animals. The large and staring eyes add to the uncanny, terrifying appearance.

The sepia or "ink" discharged through the siphon of the squid makes a dark cloud in the water and favors its escape from