190 



MOLLUSKS. 



MOLLUSKS. 



THE term Mollusk comes from a word which means 

 soft; and these animals have a soft body with no back- 

 bone nor internal skeleton ; nor is the body divided 

 into rings or joints, as in the Articulates. Most of 

 them have a hard covering called a shell, and are of- 

 ten called Shell-Fish; but they are in no way related 

 to Fishes. The shells are the parts which we oftenest 

 see ; for when the animal is dead, the soft parts soon 

 disappear, and only the shell remains. Curious and 

 wonderful as the shells are, they often give only the 

 faintest idea of the appearance of the animals when 

 alive. See the differences between Figures 356 and 



Fig. 356. Helix, alive. 



<>57, where the first represents the shell alive ^,nd the 

 animal expanded, the second the shell as when dead, 

 or when the animal is concealed 

 in the shell. It is important to 

 know that the shell is a part of 

 the animal, and not a mere house 

 which it enters arid leaves at 

 pleasure ; although it readily ex- 

 pands much beyond the limits of 

 the shell, and withdraws itself wholly within the same 



Fig. 357. Helix, dead. 



