THE OYSTER. 125 



were counted on one tile, which is shown in Plates 

 X and XL On October 10, most of these had 

 grown to a size of three-quarters of an inch, as shown 

 in Plates XIV and XV. 



Attempts to collect spat by artificial means are not 

 always successful, and experience has shown that 

 clean collectors are essential, and that failure is usu- 

 ally due to the presence of mud or other sediment 

 upon their surface. As this sediment accumulates very 

 rapidly, and as an extremely thin layer is enough 

 to prevent the young oysters from becoming firmly 

 fastened, it is important that the shells or other sub- 

 stances which are employed be perfectly clean, and 

 that they be not put into the water until spawning 

 has commenced. 



I have made many experiments in order to discover 

 the conditions which are most favorable for a good 

 " set " of spat, and I have satisfied myself that those 

 collectors are most reliable which are nearest the sur- 

 face of the water. They are much less exposed to 

 deposits of sediment than those in deeper water, and 

 my studies upon the embryology of the oyster have 

 shown that as soon as the embryo begins to swim it 

 comes to the surface, and swims for about two days 

 within half an inch of the top. I have been very suc- 

 cessful with floating collectors, and, in Plate XVI, I 

 have figured a boulder which had been for six weeks 

 in one of them, a few inches from the surface, and had 

 furnished a lodgment for many hundred oysters, 



