46 POPULAR SCIENCE MONTHLY. 



SHELLS. 



By MAEGARET WENTWOETH LEIGHTON. 



See what a lovely shell, 

 Small and pure as a pearl, 

 Lying close to my foot. 

 Frail, but a work divine, 

 Made so fairly well 

 With delicate spire and whorl, 

 How exquisitely minute, 

 A miracle of design ! 



Slight, to be crushed with a tap 

 Of my finger nail on the sand ; 

 Small, but a work divine ; 

 Frail, but of force to withstand, 

 Year upon year, the shock 

 Of cataract seas that snap 

 The three-decker's oaken spine 

 Athwart the ledges of rock 

 Here on the Breton strand ! 



Tennyson, 



AS we watch the little pools of water left among the rocks by 

 -^^ the retreating tide the pearly luster or the violet or golden 

 tint of some tiny shell catches our eye. How exquisite its form 

 and coloring ! 



Shells have always, from the most ancient times, been greatly 

 prized. Prehistoric men discovered in the burial caves of Au- 

 vergne have chaplets of shells which scientific men tell us they 

 must have traveled long distances to gather. It is only of late 

 years that their curious little occupants have been interviewed 

 and some ideas obtained with regard to their characteristics and 

 mode of living. 



All shells with their inhabitants belong to the immense class 

 known as Mollusca, or soft-footed animals. Shells are divided 

 into two groups univalve, those having but one valve, as the 

 snail, whelks, cowries, etc. ; and bivalve, as the oyster, clam, and 

 mussel. 



If we take the clam as a typical mollusk we shall see that each 

 little line on the inside or outside of the shell reveals an inter- 

 esting fact. On the outer surface of each valve are a number of 

 concentric lines parallel to the edge and growing fainter toward 

 the hinge part. These are called the lines of growth, and are 

 made by the mantle. The clam's mantle is quite as useful to him 

 as are our hands to us, and he uses it for similar purposes. The 

 mantle surrounds the clam's body inside the shell, its edge pro- 



