GASTEROPODS. 169 



cowry, a small species of porcelain shell is used in Africa 

 and India as money. Some shells are made up of layers 

 having different colors, and are used to make large 

 cameos. Others, whose interiors are lined with a layer 

 having brilliant pearly reflections, furnish the mother- 

 of-pearl of commerce. It is probable that the famous 

 Tyrian purple was manufactured from certain of these 

 colored shells. 



^#f" 



EDIBLE SNAIL (the shell has been removed, and the animal opened through 

 the back). t, tentacles ; ph, oesophagus ; mt, muscles of the tentacles ; n, 

 cesophageal ganglia ; gs, salivary gland ; e, stomach ; ao, anterior aorta ; m, 

 mucous gland ; pp', lung and its orifice, a ; i, intestine ; o, auricle ; v, ventri- 

 cle ; F, liver ; p, foot ; r, oviduct. 



To study the internal organization of the gasteropods 

 we may select the common edible snail. After having 

 removed the shell and cut the creature open, we find a 

 stomach with salivary glands, and a large liver occupy- 

 ing the posterior portion. The heart is to the left, and 

 may be seen to beat by cutting a rather large window 

 in the shell of a snail. The egg-passage or oviduct may 

 H 15 



