44 PEARLS [CH. 



stage would never be reached. It is often quite easy 

 to provide artificial supports to which the pearl oyster 

 and other shellfish spat can attach themselves when 

 natural objects are wanting. Thus, for example, at 

 places on the French coasts, attachment areas are 

 prepared for the edible oyster and mussel. Drain 

 pipes, placed in shallow water, have served as very 

 favourable objects for the young spat of the scallop. 



The shell valves now continue to grow, increasing 

 in thickness, but retaining for some time their trans- 

 parency. The larval swimming organ becomes re- 

 duced and disappears, and the shell-closing muscles 

 and foot develop. These tiny oyster spat are only 

 about 0*1 mm. in diameter. 



If they have only sandy wastes as sea bottom it is 

 certain that their life is short. Hence there is im- 

 mense need for favourable grounds, with either hard 

 objects or with seaweeds to the fronds of which the 

 young spat can attach themselves. 



The young pearl oyster is an actively moving 

 organism, even though it attaches itself by means of 

 a byssus. In this again it resembles many other 

 common bivalves. The method of locomotion can be 

 well seen if a quite small active edible mussel or a 

 very young scallop is placed in a glass vessel of sea- 

 water. 



The animal attaches itself to the glass by means 

 of strands of byssus secreted in the way already 



