82 Laboratory Guide in Zoology 



THK FRESH-WATER SNAIL 



Fresh-water snails may be easily found at almost any 

 season of the year. In summer they are abundant on the 

 vegetation in ponds and slow-running streams, while in 

 winter they may be easily procured by scraping the bottom 

 of the pond with a collecting net. This is especially feasi- 

 ble in springs that do not freeze over. This outUne is for 

 one of the species with conical, pointed shells. Have one 

 or more specimens in the hand, and one or more live ones 

 in a beaker aquarium. 



I. — Study the specimen as a whole. Notice the three dis- 



tinctive characters of the molluscs, — the foot, the mantle, 

 and the shell secreted by the mantle. Make a drawing 

 of a side view of one with its body and tentacles 

 extended. 



II. — Study the shell. Can the animal part with it.' 

 Notice the pointed end : this is the apex. Notice the 

 open end : this is the aperture. Notice the spiral 

 groove : this is the suture. Notice the divisions of the 

 shell made by the suture : these are the whorls ; the 

 large anterior one is the body whorl, v/hile the others 

 together form the spire. The axis from the centre of 

 the aperture to the apex is the columella. Notice lines 

 around the shell parallel to the lip : these are the lines 

 of growth. 



III. — Hold the shell with the apex toward you: if the 

 suture turns to the right, the spire is a right-hand or 

 dextral spire ; if it turns to the left, it is a left-hand or 

 sinistral spire. Or hold the shell with the aperture 

 toward you : if the aperture is to the right, the shell is 

 dextral ; if to the left, it is sinistral. Which is your 

 specimen .'' 



