434 ANNUAL REPORT SMITHSONIAN INSTITUTION, 1913. 



When the shells are cut into ornaments, as many as 15 pieces, in- 

 cluding one scimitar-shaped paper knife made from the lip, or rim, 

 may be produced from one shell of about 22 inches in circumference. 

 At an average retail price of 50 cents for each of these pieces the 

 products of the shell would realize $7.50. 



The blister pearls are more or less extended elevations of the inner, 

 pearly layer of the shell, formed by the secreting cells of the mantle 

 in defense of the invading, boring mollusk, Pholadidea farva. They 

 occur mostly in the red abalone, with onlj'' one blister pearl in about 

 1,000 shells of the green or black species. A crab, which infests the 

 abalone at certain seasons, may be the cause of such formations, and 

 one exhibited the complete outline of such a crab. Frequently the 

 blister pearls are formed over sea-urchin spines, chiton, or razor-clam 

 shells, pebbles, and other foreign bodies retained beneath the mantle. 

 Sometimes a diseased visceral hump is cut off and covered by nacre, 

 making a huge blister pearl. 



The free pearls have the color of the inside layer of the shell, vary- 

 ing from white to green or pink, according to the species. They sell 

 from 50 cents for the smaller ones to $125 for one of 25 grains. 

 Occasional pearls are so large and of such fine quality as to sell 

 for five hundred or even one thousand dollars. The free pearls are 

 frequently found within the stomach. During the year 1912 over 

 86,000 blister pearls and 4,000 free pearls were obtained from the 

 abalone fishermen. 



The origin of pearls has been a matter for speculation during many 

 centuries. As related in ancient folklore, the pearl oyster, rising to 

 the surface of the sea in the early morning, opens wide the valves 

 of its shell, so that dewdrops may fall within. Under the influence 

 of the air and warm sunshine lustrous pearls develop from these 

 glistening drops of dew. The pearls are white when the weather is 

 fair, but dark if it is cloudy. This belief was held from the first 

 to the fifteenth centuries, when the theory was advanced that the 

 eggs of the pearl oyster serve as nuclei for pearls. About the middle 

 of the sixteenth century Kondelet concluded that pearls form from 

 diseased concretions, and then, in 1600, Anselmus de Boot demon- 

 strated that they are made of the same substance as the shell. Reau- 

 mur, in 1717, showed by aid of the microscope that the pearl is com- 

 posed of concentric layers of nacre, which we now know serve as 

 minute prisms to split up the white light into the rainbow tints so 

 beautiful when reflected from tlie surface of the pearl. In the mid- 

 dle of the nineteenth century from an investigation of the fresh- 

 water mussels of Turin Lake, Filippe proved that the stimulus for 

 pearl formation in that species is a trematode worm. Other natural- 

 ists, Kiichenmeister, 1856 ; Mobius, 1857 ; Kelaart and Humbert, 1859 ; 

 Garner, 1871; Dubois, 1901; and Giard, 1903, have contributed to 



