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. 
