166 CLASS-BOOK OF ZOOLOGY. 



710. How many eggs does one Oyster produce, and at what time? 



711. What is the size and form of the Pearl-oyster, and where is it 

 found ? 



712. Why. is ii remarkable? 



713. Where are the Pearl-fisheries in Asia, and where are Pearls in 

 America obtained? 



714. How are the shells of the Pearl-oyster obtained, and what are the 

 dangers of the Pearl-fisheries? 



715. What is the yalue of precious Pearls ? 



716. What does Pliny relate in regard to precious Pearls? 



717. What is the amount of the importation of Pearls and Mother- 

 of-Pearl into China? 



718. What do you know of Soft-water Shells? 



(section XLIII. CONTINUED.) 



§ 719. The Univalve Shellfish, the body of which is 

 enclosed in a single shell, are still more perfect than the 

 Bivalves, for they are provided not only with arteries, 

 veins, a heart and liver, but also with a head and two 

 eyes, and at its anterior extremity, with two retractile 

 tentacula, (thread-like projections upon the head,) as the 

 Snail, Cuttle-hsh, Nautilus, etc. 



§ 720. Among the Univalve Shells, the Cowry (Cy- 

 praea Moneta) is deserving of notice, from the use made 

 of it as money in the East Indies, the South Sea Islands, 

 and by the nations on the coast of Africa. 



\ 721. In Bengal, 2.500 are worth about one quarter of 

 a dollar ; and yet there are articles in the markets which 

 may be bought for a single Cowry — Areca-nuts, for ex- 

 ample. 



\ 722. The Cowry is a porcelain-like shell of a pale- 

 yellow color, sometimes with an orange-colored ring on 

 the back, and white below ; it is scarcely an inch long, 

 and about the thickness of a finger. 



§ 723. The Whelk, (Buccinum,) with its different 

 species, has the form of a helmet ; as, for instance, the 

 Harp, (Buccinum Harpa,) distinguished by its beautiful 

 flesh-color, mixed with brown and white spots. 



\ 724. The eggs of many species of the Whelk are 



