HABITS OF MARINE ANIMALS 147 



Some years ago I spent three days upon an oyster 

 farm, and after the work I saw done there, I came 

 away wondering how it was that oysters were so cheap. 

 On my arrival, I was informed that a great many of 

 the oysters were " white sick," which meant that on 

 opening the valves there exuded from the mantle - 

 cavity a liquid, creamy fluid, which consisted of millions 

 of embryo oysters. At this stage the embryo is devoid 

 of pigment, only partially covered by the primitive 

 shell, and has at one end of it numerous hair-like 

 filaments, known as cilia. 



We dredged, and at last brought up a " black sick " 

 oyster, the difference being that the embryos in this 

 specimen were now pigmented, and the two delicate 

 valves completely covered the developing oyster. 



Once an oyster is black sick, at any time the young 

 ciliated embryos, known as spat, may be blown out of 

 the mantle-cavity of the parent into the sea. Scrape a 

 slate pencil and drop the dust into a tumbler of water 

 and you see exactly the appearance of the spat to the 

 naked eye when first set free. 



I spent many hours trying to get a photograph of 

 spat being blown out, but did not succeed. However, 

 as the process is exactly similar in appearance to a 

 scallop blowing out a cloud of sperms, of which I have 

 a series of illustrations, I show a scallop instead. In 

 both cases the valves open slightly more than in the 

 resting position, and then shut with a snap, and each 

 time a cloud is shot out, like smoke from a gun. 



