Page:Popular Science Monthly Volume 20.djvu/160

Rh resulting young are exposed, unprotected, to all the vicissitudes of climate and to the ravages of all enemies.

After the formation of the shell, and the development of the locomotive powers, the young of both varieties begin their search for a permanent resting-place or point of attachment. The swimming period is of short duration, and the powers of locomotion are not very great; consequently, such points of attachment must soon be obtained, or the young oyster perishes. Any moderately rough, hard substance, provided that the surface is clean, is suitable for attachment, and such objects, when exposed for the purpose of attracting the young brood, are called "cultch." Pieces of wood, boughs of trees, planks, stones, old shells, tiles, and fagots, have all been successfully used. It is only necessary that the surface should be hard and clean, and, if dark colored, so much the better. Upon finding the "cultch," the "spat" attaches itself firmly, and is thenceforward, so far as its own power is concerned, located for ever; all future movement and change of position are due to causes, natural or otherwise, over which it has no control.

The development now is one of ordinary growth, the animal having passed through its embryonic life; its organs are formed and are in active operation; it is but immature. The increase in size and the development of the different parts, or, in other words, the growth, are much more rapid with the American variety than with the European. Though we have no record extending over any length of time, and none of different localities, yet the observations during the summer of 1879 in Chesapeake Bay show that in the first three months of existence the oyster in that locality increases in size from a hardly visible speck to an average length of one and a quarter inch, and a few were over two inches long. The lower and attached side grows the most rapidly, and during this first period the growth is mainly in length; there is, of course, a development in all directions, but the greatest is toward the lips of the shell. After the first year, the increase in size is not so rapid, and oysters of two or three years of age are about two inches broad and three inches long, though those dimensions will vary considerably in different localities on account of the different conditions to which the animals are subjected; in three years at the most the American oyster is considered mature, and will present all the characteristics of those found in the markets. With the European variety the growth is much slower, and at maturity they are very much smaller than the American oyster: but this difference is immaterial to the question under consideration, and all that is necessary to notice is the consequence of the different methods of propagation.

With all animals Nature strives to provide against the destruction of the young after birth by insuring a sufficient number to allow for all ravages; and the greater the dangers to which the immature of any species is exposed, the larger will be the number provided to meet