292 



GASTEEOPODA 



selves forward or backward, in a straight line or a 

 curved one, with equal facility. But the Heteropods 



Fig. 234.— carinaeia. 



need occasional repose, and a cessation from activity ; 

 and admirably is the foreseen want provided against. 

 Where are they to rest? Where fix their anchor 

 in the world of unstable water around them ? They 

 are created to live, and are born amidst the fields of 

 seaweed, which voyagers describe with amazement, 

 as covering leagues of sea within the tropics ;* and to 

 enable them to attach themselves to the narrow 

 leaves of this " gulf weed " {Sargassuni), they are 

 furnished with a small sucker, which, like a cupping- 

 glass, applied against the surface of the leaf, suspends 

 them without exertion. This little sucking disk is 

 situated on the upper and hinder margin of the 

 fin. — Dr. Johnston. 



* The gulf-weed forms a floating continent. In steering toAvards 

 the equator it is usually first observed in fields and islands near the 

 coast of Madeira, whence it spreads to the Gulf of Mexico, and the 

 Caribbean Sea. After sweeping round these shores, it escapes by 

 the Gulf of Florida, whence it progresses towards the Azores. 

 There is a similar circulation of gulf- weed in the southern hemi- 

 sphere. 



