238 ZOOLOGY. 



To what does the animal adhere in the water ? Must it have 

 solid support? Can it swim? What is its method of locomo- 

 tion? What does it eat, and how? Can you determine whether 

 it uses the air in breathing or gets its oxygen from the water? 

 Proof? How is the gliding motion effected? Watch, with -a 

 lens, one crawling along the side of the glass vessel. Record 

 signs of sensitiveness to stimuli, by experiments of your own 

 devising. 



2.. General Form. Is there any sign of bilateral symmetry? 

 In what parts? How are anterior and posterior distinguished? 

 Relation of the shell to the animal ? Identify : 



Head : tentacles, number and position ; eyes, number and 

 position. 



Foot, the muscular expansion : shape, changes in form and 

 position. 



Mouth. 



Respiratory orifice, position. Under what circumstances 

 seen? 



3. Shell (secure empty ones). Make sketches of the shell 

 and identify the structures referred to in the following terms: 

 apex, aperture, lip, spire, whorl, suture, columella. (See 

 Fig. 1 08). 



How would you describe the direction of the spiral? How 

 many whorls ? Have the young and old the same number ? Can 

 you detect lines of growth? 



4. Soft Parts. These may be removed by dropping the animal sud- 

 denly into hot water, and then gradually twisting the soft portion from 

 the shell. It will scarcely repay the trouble to do more than re-identify 

 the following parts : mouth, respiratory orifice, mantle and mantle chamber, 

 and collar (a portion of the mantle). The spiral is occupied by the diges- 

 tive tract, its glands, the reproductive bodies, etc. 



5. Development. Examine the stems of plants and the sides of the 

 vessel in which snails have been kept for some days for gelatinous cap- 

 sules of eggs. They are almost transparent and the eggs may be easily 

 located. What seems to be the value of the gelatine? Number and ar- 

 rangement of the eggs? What is the shape of the eggs? Get the earliest 

 stages possible, and watch day by day at short intervals, or compare cap- 

 sules of different ages. If care is taken, some idea of the early seg- 

 mentation stages may be obtained. Look for the blastula : are the cells of 



