CLASS-BOOK OF ZOOLOGY. 165 



in the pursuit, incur the risk of life in the occupation. 

 The diver is constantly in peril from suffocation and 

 sharks ; while the oysters, exposed to the sun, and putre- 

 fying in numberless quantities, produce diseases, by 

 which thousands of those employed are carried off in a 

 few weeks. 



§ 715. The value of pearls is estimated according to 

 their size, the larger ones being as valuable as the most 

 precious stones. A pearl weighing one grain is sold for 

 one dollar; but a very large one has brought $10,000; 

 and one which the Venetian Republic presented to the 

 Turkish emperor, was valued at $100,000. 



§ 716. Precious pearls commanded in Rome a price 

 beyond that of all other luxuries ; and Pliny relates that 

 a certain Lolia Paulina, the grand-daughter of a Roman 

 proconsul, or governor, was seen at a dinner-party, having 

 her head, neck, ears, and fingers ornamented with pearls, 

 the value of which was estimated at a million of dollars. 



5 717. The importation of precious pearls into China 

 amounts every year to $25,000, and that of mother-of- 

 pearl to $70,000. 



§ 718. The Soft-water Shells are brown, oval, flat, 

 and horny, and are found in rivers and canals. 



QUESTIONS ON SECT. XLIII. 



693. What are Shellfish? 



694. How is their shell formed? 



695. Why are many of the shells deserving of notice ? 



696. In what respect are they more perfect than the preceding 

 Orders ? 



697. What is called the foot of the Shellfish ? 



698. Why has Providence covered them with hard shells? 



699. What do they eat? 



700. Into what families is the Order of Shellfish divided? 



701. Describe the body of a Muscle. 



702. What is the size of the Stone-piercer, and where is it found? 



703. What do you know of its respiratory tubes? 



704. In what respect is it injurious or usefid? 



705. Why is it obliged to bore holes, and how may the fact be ex- 

 plained ? 



706. Describe the Razor-shell. 



707. What do you knew of its abode, use, and the manner of catch- 

 ing it? 



708. What is the use of the Oyster, and where is it found ? 



709. What do you know of the egg and growth of the Oyster? 



