SEA SHELLS THAT BUILD NESTS. 



197 



a mermaid as it swims through the water. Swim ? 

 Certainly it can swim, or better, perhaps, fly .through 

 the water, using the two valves forming the shell ex- 

 actly as some butterflies of the extensive genus Pam- 

 jphila, popularly called "skippers," from the short, 

 jerky character of 



'v. 





o^ 



U^ 



^ 



their flight, use 

 their wings. 



TThen resting 

 upon the sea bot- 

 tom the lima opens 

 wide the valves 

 of the shell, as 

 these butterflies do 

 when basking in 

 the sun, but when 

 disturbed flaps its 

 light shells and 

 darts away. As 

 the shellfish settle 

 quietly on the bot- 

 tom again, they "anchor themselves securely," says 

 Prof. Kingsley, describing them, " by means of their 

 provisional byssus, which they seem to fix with much 

 care and attention, previously exploring every part of 

 the surface with their extraordinary leechlike foot." 



The byssus, it may be remarked, is a most singu- 

 lar provision of Xature, a silky bundle of fibers, from 

 which the historian Gibbon said the old Eomans 

 wove a costly fabric. This tuft of long filaments is 

 formed by a gland in what is called the foot of the 



Lima : a sea shell that builds a nest. 



