694 REPORT OF COMMISSIONER OF FISH AND FISHERIES. [12] _ 
lobe consists of two plates, which grow together above and below. The mantle-folds 
and the gills taken together form the so-called ‘‘ beard” of the oyster. In the spaces 
between the layers of the beard the development of the eggs takes place. In the fig- 
ure a few germs are represented in this brood-cavity. 
Now, a mature egg-bearing oyster (Fig. 4) lays about one million of eggs, 
so that during the breeding season there are upon our oyster-b eds at least 
2,200,090,000,000 young oysters, which surely would sutiice to transform 
the entire extent of the sea-flats into an unbroken oyster-bed ; for if such 
a number of young oysters should be distributed over a surface 74 kilo- 
meters long by 22 broad, 1,351 oysters would be allotted to every square 
meter. But this sum of 2,200,000,000,000 young oysters is undoubtedly 
less than that in reality hatched out, for not only do those full-grown 
oysters which are over six years of age spawn, but they begin to pro- 
pagate during their second or third year, although it is true that the 
young ones have fewer eggs than those which are fully developed. Ata 
very moderate estimation, the, total number of three to six years old 
oysters which lie upon our beds will produce three hundred billions of 
eggs. This number added to that produced by the five millions of full- 
erown oysters would give for every square meter of surface not merely 
1,351 young oysters, but at least 1,535. In order to determine how many 
eges oysters produce, they must be examined during their spawning sea- 
son. This begins upon the Schleswig-Holstein beds in the middle of 
June, and lasts until the end of August or beginning of September. The 
spawning oyster does not allow its ripe eggs to fall into the water, as 
do many other mollusks, but retains them in the so-called beard, the 
mantle, and gill-plates (Fig. 5) until they become little swimming ani- 
mals (lig. 7). Theeggs are white, and cover the mantle and gill-plates 
as a semi-fluid, cream-like mass. As soon as they leave the generative 
organs the development of the germ begins. The entire yolk-mass of 
the egg divides into cells, and these cells form a hollow, sphere-like body, 
in which an intestinal canal arises by the invagination of one side (Fig. 7). 
Very soon the beginnings of the shell appear along the right and left 
sides of the back of the embryo, and not long afterwards a ciliated pad, 
the velum, is formed along the under side. This velum can be thrust out 
from between the valves of the shell at the will of the young animal, 
and used, by the motion of its cilia, as an organ for driving food to the 
mouth, or, in swimming, as a rudder. During these transformations 
the original cream-white color of the germ changes into pale gray, and 
finally into a deep bluish-gray color. At this time they have a long oval 
outline, and are from 0.15 to 0.18 of a millimeter in breadth. Over 
300,000 can find room upon a square centimeter of surface. If an oyster 
in which the embryos are in this condition is opened, there will be found 
upon its beard a slimy coating thickly loaded with grayish-blue granules. 
These granules are the embryo oysters, and if a drop of the granular 
slime be placed in a dish with pure sea-water the young animals will 
soon separate from the mass, and spread swimming through the entire . 
