POSITIONS OF THE SPAT. 75 T 



European Oyster, always appear to be mucli longer than wide, but many of them are almost 

 entirely exposed to the air during low tide, a rare occurrence, according to Mobius, with the 

 banks on the Schleswig-Holstein coast of the North Sea. I learned from the owners of 

 some of these banks that, although a considerable proportion of the Oysters on them were 

 at times frozen to death during the severe winters, the fecundity of those which remained was- 

 such, combined with the naturally favorable conditions found on the banks for the growth 

 of old and young, as to restore the beds to their wonted productiveness in one or two seasons. 

 Whether this description of the fecundity of the beds found in shallow water is overdrawn 

 or not matters little, since there was the plainest evidence that we had here before our eyes 

 the best natural conditions for the propagation and feeding of the individuals. The beds are, 

 in a word, natural spat-collecting grounds ; places where such conditions obtain as will allow a 

 large proportion of the swarming brood of the spawning season to afftx itself securely and survive 

 in positions where an abundance of food may be got. The tide ebbing and flowing over the beds 

 not only carries with it in suspension the microscopic food best adapted for the nourishment of the- 

 Oysters, but also tends, owing to the peculiar arrangement of the shells on the banks, to keep the 

 surface of the latter clean, so as to be well adapted as favorable points of attachment for the young.. 



In all of the natural banks which I have had the pleasure of examining in the Chesapeake,-, 

 the individual Oysters assume an approximately vertical position. The assumption of this position- 

 seems perfectly natural ; with the hinge end downwards and the free edges of the valves directed 

 upward the animals are in an excelleut position to feed, while the outside vertical surfaces of th& 

 valves are well adapted to afford places of attachment for the spat; The latter, however, appears- 

 to attach itself in the greatest abundance to the old Oysters at the surface of the bank. The result 

 is that when, one removes the Oysters from the bed they are found to adhere together in clusters,, 

 generation after generation being piled one on top of the other in succession. As many as four 

 generations may be made out in most cases ; the oldest being buried in the mud and sand below 

 and is often found to be smothered by those which have followed. Even below the last stratum 

 of living Oysters, if one teeps digging, it is discovered that thp shells of numerous still more- 

 remote ancestors of the living ones now occupying the bed are disposed vertically in the sand and 

 earth beneath. Attached to the upper edges of these dead shells follows, we will say, the flrs,t 

 living generation and so on to the fourth, composed mainly of young individuals or spat only a 

 few days or months old. Whether it is proper to regard the superimposed series of individuals as. 

 generations may be questioned, but as no more expressive word occurs to me, I wish to be under- 

 stood as using it here with qualifications. 



Positions of the spat. — The spat does not fix itself in any constant position ; the young 

 may have the hinge of the shell directed downward, upward, or to the right or left hand. 

 Singularly enough the shells do not grow in the directions which the free edges of the valves- 

 are made to assume in the young. Should the young happen to be fixed hinge downward 

 the free edges of the valves grow in length directly upward; in case the hinge is directed 

 either to the ■ right or to the left, the layers of calcic carbonate will be deposited in 

 such a way ui)on one side as to cause the free edges of the valves to be eventually 

 directed upwards, causing the umbonal portion of the valves to describe an arc of 90°.. 

 in case the hinge is at first directed upward, the layers of carbonate of lime will be deposited 

 in such a way by the mantle as to bring the mouth of the shell upward. The attempt to get 

 into a vertical position will, however, not always be successful in cases like the last; the arc of 

 180°, which it is necessary for the animal to traverse from its starting point in order to build 

 its shell with the free edges opening upward, seem to be a feat a little too difficult of accom- 

 plishment, in spite of the wonderful pei'sistence of effort manifested by the inhabitant. 



