intelligence of the male would expect) put into practice by the male parent. Thus, there is a large fish in tropical rivers which takes the eggs laid by the female into his capacious mouth, and swims about with them for three or four weeks, giving them the advantage of a current of water which runs through his mouth to his gills. When the young hatch they swim out of their fond father's mouth. The male of pipe-fishes and of the little "sea-horse" receives the eggs laid by the female into a pouch excavated along his ventral surface. There the young hatch, and are guarded by the nursing father. On the other hand, some fathers impartially eat their own young, as well as those of other parents, and the mother has a hard job to protect her offspring. A female octopus (the poulp or eight-armed cuttle-fish) sits over her eggs in a nest built of pebbles at the bottom of the sea (or of an aquarium tank in the instance studied by me many years ago at Naples), and squirts a stream of pure sea-water over them. She resents the approach of a fish or a crab or a landing-net with splendid fury and recklessness of attack. Often the males of fishes, frogs, and birds guard the eggs, or guard the nest where the female is occupied in caring for the eggs or the young.

There are various species of oysters common in all parts of the world which are eaten as delicacies. Primeval (Neolithic) man ate oysters (the common sort) in Denmark in enormous quantity-great heaps of the discarded oyster-shells are found, buried among which are discovered stone axe-heads and bits of rude pottery. In the West Indies travellers relate that the oysters "climb" the trees which overhang the water of quiet creeks and inlets of the sea. The fact is that the branches of the mangrove trees dip into the water, and the young oyster "spat" attaches itself to the immersed. twigs. After a year or two, the tree grows vigorously,

and raises its branches up in its growth, so that the oysters are carried far up above the sea waves. Of course they die under these conditions, but their position suggests the explanation that the oysters have climbed up the trees. Ship barnacles fix themselves, similarly, to the twigs of willow trees in the quiet sea lochs of the West of Scotland, and this led 500 years ago to the belief that the catkins of the willow tree ripen into barnacles. Since it was also held that the little animal of the barnacle hatches out of its shell as a young goose -the so-called "barnacle goose "-the marvellous story was believed that these geese are actually budded from willow trees. I believe that the supposed relationship of the goose and the ship's barnacle arose solely from the accidental similarity of the names of the two animals— the "bernack" goose and the sea “barnacle" being names of independent origin. The names were different originally in sound and signification, but were corrupted by fisher-folk into one and the same word. Hence a fantastic fable took its growth.

In Paris you may test and compare several local varieties of the common oyster in a celebrated oystershop. There are Courseilles, Cancales, Marennes, Ostend, Zeeland, Arcachon, English natives, Côtes Rouges (red banks), and Black Rocks. And you can eat sea-urchins there, too, if you wish. They have not, however, got the celebrated oysters from the Lake Fusaro, near Naples. This was the ancient Acherusia palus, and in the neighbouring Lake Avernus and the Lucrine lake oysters were cultivated by the ancient Romans, the young oysters being made to affix themselves at "the fall of the spat" to wooden "stands" or frames, which were then placed in the lake (a salt-water lake), where they had abundant minute vegetable food and grew large and fat. The same cultivation, with the same shape of "stands,"

is carried on at the present day in the Lake Fusaro. My friend, Mr. Günther, of Magdalen College, Oxford, has published pictures of Roman tiles from this neighbourhood showing the oysters adhering in rows to the wooden frames. These tiles were apparently sold to holiday visitors in the time of the Roman emperors as a memento of a happy day spent at the Lucrine lake, just as a sugar basin or a mug is now sold at our seaside resorts with the inscription, "A present from Margate," or Southport, or Blackpool, and the picture of a shrimp above it.

The care of the breeding oyster and the plans adopted by the owners of oyster-beds for catching the "spat," or young oysters, when they fall to the bottom, by placing movable tiles or frames for them to fix themselves to, form an important part of the craft of the oyster-man. It is a difficult business, and is variously carried out in England, France, Holland, and America. The young oysters, when they have fixed themselves, are carried on the movable tiles or frames from one region to another for the purpose of encouraging their growth and avoiding a variety of dangers to their life and health (sometimes from the Bay of Biscay to the mouth of the Thames!). They are often--but not always-finally fed up in sea-ponds or inlets, which are peculiar in containing an enormous number of those very minute microscopic plants, with beautifully shaped siliceous shells, which are known as diatoms. These are SO abundant in such ponds as to form a sort of powder or cloud near the bottom, and the oysters draw them, day and night, by their gill-currents into their mouths, digest them, and grow fine and fat. The district of Marennes, on the west coast of France, is celebrated for having seaponds or tanks in which a wonderful diatom of a bright blue colour abounds; so abundant are they that the

cloud produced by them in the pools is of a deep cobaltblue. When oysters are placed in these tanks to fatten, their gills or beards become rich blue-green in colour. They lose the colour after ten days, when removed to ordinary tanks. These are the celebrated green oysters or "Marennes vertes" of French restaurants. The colouring matter of the little diatoms-swallowed by the million and digested-is taken up by the blood of the oyster from its stomach, and is excreted by certain corpuscles on the surface of the gills-as I showed some twenty-five years ago—just as red madder is deposited in the bones of a pig fed upon madder, and as the feathers of the canary take up the colour of cayenne pepper when it is mixed with the canary's food. It used to be thought that the green colour of the green oyster is due to copper-and that opinion was supported by the curious fact that the blood of all oysters and other molluscs, and also of lobsters, scorpions, and king-crabs, does really contain a minute quantity of copper, just as our blood contains iron! It was also supported by the fact that occasionally a fraudulent fishmonger, when asked to supply green oysters, has been convicted of colouring the beards of ordinary oysters with green copper salt, so as to imitate the real article! The real history of the green-bearded oysters is now quite certain, and any one interested in the matter should look at the coloured pictures of the beautiful little blue-coloured Navicula ostrearia-the diatom on which this oyster feeds, published by me in the Quarterly Journal of Microscopical Science in 1885.

XV

MATERNAL CARE AND MOLLUSCS

THE

HE American and Portuguese species of oysters, which are called respectively Ostrea virginiana and Ostrea angulata, as opposed to the common oyster, which is known as Ostrea edulis, are not hermaphrodite like the latter, but have distinct males and females. Moreover, the young are not fertilised within the parent's body, nor do they pass their earliest stages of growth within the parent's shell adhering to the "beard," or gills, as in the common oyster. The eggs (Fig. 31) are, on the contrary, discharged by the females into the sea, and at the same time the males discharge a cloud of microscopic sperm filaments, or spermatozoa (Fig. 32), which dart about in the water and fertilise the eggs. That is a more prodigal and less certain process than that pursued by the common oyster. The American and Portuguese oyster have to pay for it. The female produces in one season not a million eggs, as does the common oyster, but nine millions. And out of every fifty million so produced (in some five or six years) only a single male and a single female individual, taking the whole oyster population of these species into consideration, survive to maturity.

This enormous excess of egg-production in order to ensure the survival of a single pair to replace their