[27] FISHERIES OF THE UNITED STATES. 211 



essential that the egg should be fertilized very quickly, for the unfertil- 

 ized egg is destroyed by the sea- water in a very short time. The next 

 period of great danger is the short time during which the embryos swarm 

 to the surface of the water. They are so perfectly defenseless, and so 

 crowded together close to the surface, that a small fish, swimming along 

 with open mouth, might easily swallow in a few mouthfuls a number equal 

 to the human population of Baltimore. They are also exposed to sud- 

 den changes of temperature, and as my experiments have shown that a 

 sudden fall in temperature is fatal to them at this time, the number which 

 are destroyed by cold rains and winds must be very great indeed. 



"As soon as they are safely past this stage, and scatter and swim at 

 various depths, their danger from accidents and enemies is greatly 

 diminished, and their chance of reaching maturity increases hundreds, 

 and probably thousands, of times. 



"Although the mortality at these early stages is so excessive, the 

 number of young which pass through them safely without help is very 

 great, and if there were no other dangers and uncertainties there would 

 be no need of measures for their protection. As they swim to and fro 

 in the water, they are carried to great distances by the tides and cur- 

 rents and reach all parts of the region of water in which the parent bed 

 is situated. In a favorable year a floating plank or bush, or piece of 

 drift wood, will be found to become covered with small oysters which 

 have fastened to it, although it may not be within miles of any natural 

 oyster-bank. The fact that the young may be collected in this way in 

 any part of the Chesapeake Bay shows that the young oysters must set- 

 tle down upon the bottom in nearly all parts of the bay, and we should 

 expect the adults to have an equally general distribution. This is far 

 from the case, and nothing could be farther from the truth than the 

 idea that the bottom of the waters of the oyster regions is uniformly 

 covered with oysters, and that it is only necessary to throw a dredge 

 overboard and drag it along the bottom for a short distance in order to 

 bring it up full. Nothing could be a greater mistake, for both in this 

 country and in Europe the oysters are restricted to particular spots, 

 'beds' or 'banks,' which are as well defined and almost as sharply lim- 

 ited as the tracts of woodland in a farming country. These beds are 

 so well marked that they can be laid down on a chart or staked out with 

 buoys; and even in the best oyster regions they occupy such an incon- 

 siderable part of the bottom that any one ignorant of their position 

 would have very little chance of finding oysters by promiscuous dredg- 

 ing. Although the young are distributed every year by the tides and 

 currents to all parts of the bottom, the dredge very seldom brings up 

 even a single oyster outside the limits of the beds. 



"The restriction of the oysters to certain points does not appear to 

 depend upon the supply of food, or upon the character of the water, 

 but almost entirely upon the nature of the bottom. The full-grown 

 oyster is able to live and flourish in soft mud, as long as it is not buried 



