228 ECONOMIC ZOOLOGY AND ENTOMOLOGY 



ally prepared collectors, the transplanting and caring for the 

 seed and the final marketing of the oyster after it has been 

 fattened and often flavored to suit the taste of a fastidious 

 public, furnishes employment to many people along the sea 

 coasts. 



Many other species occur in other parts of the world, where 

 they are usually important articles of food. 



Shell-fish and Disease. In feeding, the oysters, clams and 

 mussels may take into their body any minute particles that are 

 to be found in the water where they are lying. Thus it will be 

 seen that any impurities that are in the water may readily 

 affect the bivalves living in it. It sometimes happens that 

 oyster or clam beds are situated so near the outfalls of sewers 

 from some city that the water is always polluted. Shell-fish 

 coming from such places are usually plump and look most in- 

 viting, but as they may contain typhoid germs and other dan- 

 gerous organisms they are to be avoided. The interest that 

 has been aroused in this subject during the last few years has 

 been the cause of much careful study, and, while the danger is a 

 very real one, the rigid supervision that is now kept over many 

 of the sources from which this important food supply comes, 

 makes most shell-fish safe. If they are thoroughly cooked 

 before being eaten the harmful organisms are destroyed. Oy- 

 sters that have been "freshened" or bloated by being trans- 

 ferred to fresher water for a few days or hours should never be 

 eaten raw, as the places where this process is carried on are too 

 often in dangerous proximity to sewer outfalls. A strong 

 public sentiment against such practice will insure its discon- 

 tinuance. 



Pearl-oysters. The "pearl-oyster" of the South Seas is 

 really not very closely related to our oysters. It is more of the 

 shape of our common pectens, and has a strong byssus by 

 which it attaches itself, at least during its earlier stages, to 

 rocks or corals. The shell of some species is quite heavy, and 

 the wonderfully iridescent inner layer is known as " mother-of- 

 pearl." The pearl-shells form an important article of com- 

 merce, as the mother-of-pearl is used in the manufacture of 

 many articles. The pearls themselves, which are formed in 



