164 CLASS-BOOK OF ZOOLOGY. 



form cloak, covered with two long shells, open at both 

 ends, and is from six to eight inches long. It is found 

 in many seas, but principally on the shores of Italy. 



§ 707. The Razor-shells conceal themselves in the 

 sand by boring perpendicular holes about three feet deep. 

 They are esteemed a palatable article of food. The fish- 

 ermen catch them at low tide by putting strong wires, 

 with a knob at the end, into their holes. The wire 

 passes between the open perpendicular standing shell, 

 which closes at the first touch of the wire, and is thus 

 thrown out. 



§ 708. The Oyster (Ostrea) is found in all parts of the 

 globe, and is everywhere considered a wholesome and 

 delicious food. 



\ 709. Oysters, like all other Shellfish, are provided 

 with shells while yet in the egg : these, which are not 

 larger than the tenth part of a line, are yearly increased 

 by the addition of a new layer, several lines broad, to 

 their margin. The Oyster, therefore, which has two 

 layers around the shell, is three years old. 



§710. The immense multiplication of oysters would be 

 incredible, if it had not been ascertained that a single one 

 produces from three to four millions of eggs ; a fact 

 which may be easily verified by means of a microscope, 

 in the months of June, July, and August, when they are 

 found within the shell, dispersed over all parts of the 

 body. 



§ 711. The Pearl-oyster (Mytilus margaritifer) is as 

 large as a man's hand, and of a roundish form. 



§ 712. It is important for the precious pearls found 

 within it, as well as for the mother-of-pearl afforded by 

 the shells. 



§ 713. There are three pearl-fisheries carried on in 

 Asia; viz. in the Gulf of Persia; in Ceylon, near the 

 town of Manaren ; and in the Island of Hainem, near 

 Japan. The Pearl-oyster is also obtained in America, on 

 the coast of Cumana, Mexico, and California. 



§ 714. These shells are found on the bottom of the sea, 

 generally at a depth of from twenty to thirty feet. They 

 are obtained by divers ; who, as well as others engaged 



