The slugs (Fig. 110) have many peculiar characteristics. If the long tentacles on the short eye stalk are destroyed, the snail will reproduce them. In winter the snails descend into the ground, or hide themselves away, literally sealing themselves in their shells by closing the door firmly, and there hibernate until spring, neither eating nor drinking, and hardly breathing during this time; if placed in a cold storage box, they will remain several years in this state. [Illustration: FIG. 109.--A snail crawling.] [Illustration: FIG. 110.--Slugs and snails.] Some of the snails of Africa are six inches across, and the eggs are an inch in length. Semper found a little snail in the Philippines, which when caught by the foot or "tail" throws it off as a lizard jerks off its tail. This is not a great hardship, as the tail is soon renewed. In a collection of shells which came from France some years ago I found several snails of different colors which were joined one to the other. The collector had cut the top from an empty brown snail and placed a living snail with a yellow shell upon it, tying the two together. The snail, supposing that its shell had been broken, immediately began to repair the wound, and closed up the breach with its shell-secreting mantle, so that the two shells became one. [Illustration: FIG. 111.--A sea slug (_Dendronotus_).] In floating on the borders of the Sargasso Sea, the vast sea of weeds in the South Atlantic, I found numbers of a beautiful sea slug (Fig. 111) which so resembled the weeds in shape and color, a rich olive green, that it was almost impossible to distinguish it, except when very close to the surface. They have attractive names, as Doris, Tritonia, Æolis, and Aplysia, and are among the wonders of the great belts of kelp which surround the continent. I once found a slug at Santa Catalina which was a vivid, almost iridescent purple; another was yellow; but the most interesting was Aplysia, a giant two feet long, which I kept in an aquarium. It weighed nearly eight pounds, could lengthen itself out to a distance of nearly three feet, or contract into a dark, olive-hued ball, scarcely six inches across. It took sea lettuce from my hand, eating with avidity, and when disturbed emitted a purple ink which filled the water and hid the monster "sea hare" from view. It laid its eggs on the sides of the tank in long chains, but if not well fed, exhibited a decided cannibalistic tendency, devouring its own progeny. This animal had an enormous foot by which it crept rapidly along, and it invariably protected itself by imitating the color of the bottom upon which it rested. [Illustration: FIG. 112.--_Onchidium_, a sea slug with eyes on its back.]