Most of our readers have heard of the fish popularly known as the Miller's Thumb, the origin of the name of which Mr. Yarrell has thus explained:--"It is well known that all the science and tact of a miller is directed so to regulate the machinery of his mill that the meal produced shall be of the most valuable description that the operation of grinding will permit, when performed under the most advantageous circumstances. His ear is constantly directed to the note made by the running stone in its circular course over the bedstone, the exact parallelism of their two surfaces, indicated by a particular sound, being a matter of the first consequence; and his hand is constantly placed under the meal-spout to ascertain, by actual contact, the character and quality of the meal produced, which he does by a particular movement of his thumb in spreading the sample over his fingers. By this incessant action of the miller's thumb, a peculiarity in its shape is produced, which is said to resemble exactly the shape of the _river bull-head_, a fish constantly found in the mill-stream, and which has obtained for it the name of the Miller's Thumb." M. Coste has constructed a kind of marine observatory at Concarneau (Finisterre) for the purpose of studying the habits and instincts of various Sea-fish. A terrace has been formed on the top of a house on the quay, with reservoirs arranged like a flight of steps. The sea-water is pumped up to the topmost reservoir, and thence flows down slowly, after the manner of a rivulet. The length is divided into 95 cells by wire net partitions, which, allowing free passage to the water, yet prevent the different species of fish from mingling together. By this ingenious contrivance each kind lives separate, enjoying its peculiar food and habits, unconscious of its state of captivity. Some species, such as the Mullet, the Stickleback, &c., grow perfectly tame, will follow the hand that offers them food, and will even allow themselves to be taken out of the water. The Goby and Bull-head are less familiar. The Turbot, which looks so unintelligent, will, nevertheless, take food from the hand; it changes colour when irritated, the spots with which it is covered growing pale or dark, according to the emotions excited in it. But the most curious circumstance concerning it is, that it swallows fish of a much larger size than would appear compatible with the apparent smallness of its mouth. Thus, a young Turbot, not more than ten inches in length, has been seen to swallow Pilchards of the largest size. The Pipe-Fish has two peculiarities. These fish form groups, entwining their tails together, and remaining immoveable in a vertical position, with their heads upwards. When food is offered them, they perform a curious evolution--they turn round on their backs to receive it. This is owing to the peculiar position of the mouth, which is placed under a kind of beak, and perpendicular to its axis.