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enemies almost as much as its swiftness (Fig. 205). The squid sometimes approaches a fish with motion so slow as to be imperceptible, and then suddenly seizes it, and quickly kills it by biting it on the back behind the head.

The octopus is more sluggish than the squid. Large species called devilfish sometimes have a spread of arms of twenty-five feet. The pearly nautilus (Fig. 206) and the female of the paper argonaut (Fig. 207) are examples of cephalopods that have shells. The cuttlefish is closely related to the squid.

(Shell sawed through to show chambers used when it was smaller, and siphuncle, S, connecting them. Tentacles, T.)

(female).

× 1/3 (i.e. the animal is three times as long and broad as figure).

(male). × 1/2.

General Questions.—The living parts of the mussel are very soft, the name mollusca having been derived from the Latin word mollis, soft. Why is it that the softest animals, the mollusks, have the hardest coverings?

To which class of mollusks is the name acephala (headless) appropriate? Lamellibranchiata (platelike gills)?