CLASS CJEPHALOPHOilA. 



48 



blood, appear as papillae, in some species, of the brightest 

 colors, and often covering the upper portion of the body. 

 A shell, present in the young, is entirely 

 absent in the adult. 



FIG. B2. 



Do' ris pi Id' sa. 

 The "gills" are arranged 

 in the form of a star. 

 Anteriorly are seen the 

 club-shaped tentacles. 



FIG. 03. 



ORDER PULMONATA (pul mo na'ta). 



The Pulmonifera (pul mo nif'er a), or 

 Lung -bearers, comprise many fresh- 

 water and land Snails, without gills. 

 The "lung" is little more than a mere 

 cavity, communicating with the exterior through a valve. 

 A single swoop of the net, through the aquatic vege- 

 tation of some of our streams or ponds, 

 will often secure a score or more of small 

 dark colored snails, which, if placed in a 

 tumbler of water, will reveal many in- 

 teresting traits. They frequently come to 

 the surface for fresh air, and if a green 

 deposit gathers on the glass, the action of 

 the jaws and odontophore can be observed, 

 as the animal scrapes this off for food. Closely allied to 

 the Pond-snails is the com- 

 mon Land-snail, or Helix 

 (he'lix). This animal is pro- 

 vided with four retractile 

 tentacles, the larger pair 

 with eyes at their extrem- 

 ity. 



Slugs are often found 

 under damp boards, and 

 are sometimes of considerable size. 



A Dextral and a Sinis- 

 tral Fresh-water Uni- 

 valve.* 



FIG. C4. 



He'lix alboll'bris. Land-snail, f, Foot. 0, 

 Mouth. E, Tentacles, terminated by the eyes. 



They show on their 



* The greater number of Cephalophorous Mollusks have the opening in the 

 shell turned toward the right, i e., they are dextral. 



