Thus we see that the spawn of the oyster is well matured before it leaves the protection of the parental shell; and by the aid of the microscope the young animal can be seen with its shell perfect and its holding-on apparatus, which is also a kind of swimming-pad, ready to clutch the first “coigne of vantage” that the current may carry it against. My theory is, that the parent oyster goes on _brewing_ its spawn for some time—I have seen it oozing from the same animal for some days—and it is supposed that the spawn swims about with the current for a short period before it falls, being in the meantime devoured by countless sea animals of all kinds. The operation of nursing, brewing, and exuding the spat from the parental shell will occupy a considerable period—say from two to four weeks. It is quite certain that the close-time for oysters is necessary and advantageous, for we seldom find this mollusc, as we do the herring and other fish, full of eggs, so that most of the operations connected with its reproduction go on in the months during which there is no dredging. As I have indicated, immense quantities of the spawn of oysters are annually devoured by other molluscs, and by fish and crustaceans of various sizes; it is well, therefore, that it is so bountifully supplied. On occasions of visiting the beds I have seen the dredge covered with this spawn; and no pen could number the thousands of millions of oysters thus prevented from ripening into life. Economists ought to note this fact with respect to fish generally, for the enormous destruction of spawn of all kinds must exercise a very serious influence on our fish supplies. I may also note that the state of the weather has a serious influence on the spawn and on the adult oyster-power of spawning. A cold season is very unfavourable, and a decidedly cold day will kill the spat. [Illustration] [Illustration] Some people have asserted that the oyster can reproduce its kind in twenty weeks, and that in ten months it is full-grown. Both of these assertions are pure nonsense. At the age of three months an oyster is not much bigger than a pea; and the age at which reproduction begins has never been accurately ascertained, but it is thought to be three years. I give here one or two illustrations of oyster-growth in order to show the ratio of increase. The smallest, about the dimensions of a pin’s head, may be called a fortnight old. The next size represents the oyster as it appears when three months old. The other sizes are drawn at the ages of five, eight, and twelve months respectively. Oysters are usually four years old before they are sent to the London market. At the age of five years the oyster is, I think, in its prime; and some of our most intelligent fishermen think its average duration of life to be ten years. [Illustration]