VARIETY OF MOLLUSCA. 



183 



Those which love deep water, are arrested by shoals : 

 others adapted to shallow seas cannot traverse un- 

 fathomable abysses. 



A few species have an immense rang'e : one is found 

 in the West Indies, Brazils, the Red Sea, Trancobar, the 

 Chinese Sea, and in one of the South Sea islands : a 

 Mediterranean shell occurs also in South Africa, the 

 Isle of France, the East Indies, China, the South 

 Seas, and even as far west as Tahiti ; and another in- 

 habits the seas of England, Guadaloupe, and the Cape 

 of Good Hope. 



The janthina, mentioned in a former page, has wan- 

 dered into almost every tropical and temperate sea. 

 Admirably adapted to float, it has not only dispersed 

 itself thus universally, but it has disseminated other 

 species, which attach themselves or their eggs to its 

 shell. An eminent naturalist possesses specimens bear- 

 ing more than one species of barnacle ; and one of them 

 is so laden with these creatures and numerous eggs, 

 that all the upper part of its shell is invisible. 



The mode in which some of these creatures are dif- 

 fused is worthy of attention. Snails and mollusks 

 generally are slow in their movements, but they are 

 not without means of extending themselves rapidly over 

 a wide space. Some lay their eggs in a sponge-like 



