21 



right handed dextral shell, Helix, Limnaea, in this position the aperture 

 is to the right of the axis. Or imagine such a shell a spiral stair-case, 

 as you ascend, ttte axis of the spire will always be on your left. Can you 

 find any left-handed (sinistral) shells ? (Physa). All whorls nearly in the 

 same plane, (Planorbis). How many whorls are there in the spiral ? 

 (The largest is the body-whorl, where most of the soft body of the snail 

 is protected, the rest is the spire.) 



Observe the lines of growth running parallel with the opening in 

 the shell. Note the color and surface markings. Can you see, a few 

 well-marked lines often separating off areas of different depths of color ? 

 These each distinguish one year's growth from another. How old are 

 your specimens ? 



Break out a piece of the shell from the edge of the body whorl. Is 

 the gap filled in, or is the new piece of the same color as the rest of the 

 shell ? Try the same experiment again removing parts of shell from the 

 body-whorl, not from the edge but from the spire. How long does 

 reparation require ? Is there any protective coloration ? 



2. Locomotion. Snails and slugs belong to the class Gastropoda 

 (bellyfooted) as foot is on the ventral surface of the body. Let snail 

 crawl on a piece of glass, and watch its movements from the under side 

 with a lens. Do you see a wavelike motion? Which way do the waves 

 move ? Why can snail hold on to a surface so firmly ? 



3. Head. How many horns on the head ? Describe them. Where 

 are the eyes. Are some of the tentacles more sensitive to touch than 

 ot;hers ? Watch mouth and its motions. Observe how it feeds. Can 

 you see tongue (radula) as a Helix rasps off the epidermis of a lea ? 

 (The radula ribbon is covered with thousands of minute sharp teeth). 



4. Respiration. Observe the opening to the lung on the right side 

 of the body. What movements of the aperture occur ? Will Helix live 

 in water ? Will Limnaea live long totally submerged, and completely 

 deprived of air ? 



5. Food. Try feeding experiments with Helix, Limax, and Limnaea. 

 Try leaves, dry leaves, soap, dead bodies of snails and slugs, and other 

 species; lichens, mayflies, coleoptera ; raw beef, fungi. Will Limax bite 

 vour hand ? Try tender skin "between fingers. 



6. Regeneration. Do lost tentacles, eyes, parts of the foot grow out 

 again if cut off ? 



XXXIV. The Sundew. 



1. Observe the habitat and general habit of the sundew. 



2. Draw a leaf, showing the tentacles. 



3. Grow sundew in shallow wooden dishes containing peat, and kept 

 in a room at a temperature of 70 degrees F. 



4. "Place pieces of rotten wood, boiled meat, or boiled egg, or bits 

 of glass no longer than a pin head, on the tips of the glands of the ten- 

 a«les at the margin of the leaves," and watch the result. 



