[Illustration: FIG. 108.--The giant yellow slug of California, _Ariolimax californica_. This slug reaches a length when outstretched of 12 inches. (From living specimen.)] =Snails, slugs, nudibranchs and "sea-shells" (Gastropoda).=--TECHNICAL NOTE.--Pond-snails can be readily found clinging to submerged stems, leaves, or pieces of wood in almost any pond. Collect some and carry alive, in a jar of water, to the schoolroom. Observe the habits of these live snails in the school aquarium. Note the movements, the coming to the surface to breathe, the eating (by scraping the surface of the leaves with the "radula" or tongue; provide fresh bits of cabbage or lettuce-leaves), the use of the feelers. Make drawings illustrating these habits. Examine the shell; note that it is univalved, that is, composed of one piece. Do the whorls of all the shells turn the same way? Make a drawing of the shell, naming such parts as the apex, spire (all the whorls taken together), the aperture, the columella (the axis of the spire), the lip (outer edge of the aperture), the lines of growth (parallel to the tip), the suture (the spiral groove on the outside). Examine the snail; note the character of the foot; note the protrusible tentacles or feelers, the eyes (dark spots at bases of the tentacles), the mouth, the respiratory opening (on right side of body in the edge of the mantle which protrudes beneath the lip when the snail's body is extended), the radula or ribbon-like tongue with fine teeth. Compare with the body of the mussel. Slugs may be found during the day concealed under boards or elsewhere; they are nocturnal in habit. If specimens can be obtained, compare with the pond-snails, noting the absence of a shell, and the fleshy mantle on the dorsal surface near the head; note the presence of two pairs of tentacles (the eyes being at the tips of the second or hinder pair), and the respiratory pore. Note the streak of mucus left by the slugs in crawling about. Some sea-shells can be got from private collections of "curios" to illustrate the variety of form of the univalve shells.