252 ELEMENTARY ZOOLOGY 



do great damage to wharves and ships. In Holland 

 where they were first discovered they caused such injuries 

 to the piles and other submerged wood which supported 



FIG. 108. The giant yellow slug of California, Ariolimax californica. 

 This slug reaches a length when outstretched of 13 inches. (From 

 living specimen.) 



the dikes and sea-walls that they seriously threatened the 

 safety of the country. 



Snails, slugs, nudibranchs and " sea-shells " (Gas- 

 tropoda). 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 aqua- 

 rium. 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 draw- 

 ing 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 ex- 

 tended), 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 ob- 

 tained, 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- 



