"In reference to some observations by Mr. Yarrell, in the _Zoological Journal_, relative to the distinction between the sprat and the young of the pilchard and herring, I can state that Cornish fishermen term the young of both the latter fishes sprats; but, how far this should go in determining the judgment of a naturalist will appear, when I add that I have never seen above one specimen of the genuine sprat in Cornwall, and that was brought me by a fisherman, to be informed what fish it was. In taking fish out of his net by night, he felt it to be neither a pilchard nor a herring, and supposed it something rare." * * * * * STRUCTURE OF BIRDS. Birds may be said to constitute an isolated class of beings. They are distinguished by certain characters from all other animals: their classification does not pass into any other, and cannot, therefore, be consistently introduced into the supposed chain or gradation of natural bodies. The skeleton or bony frame of birds is in general lighter than in quadrupeds. They have the largest bones of all animals, in proportion to their weight; and their bones are more hollow than those of animals that do not fly: air-vessels also enable them to blow out the hollow parts of their bodies, when they wish to make their descent slower, rise more swiftly, or float in the air. The spine is immovable, but the neck has a greater number of bones, (never less than nine, and varying from that to twenty-four,) and consequently of joints, and more varied motion, than in quadrupeds. The breast-bone is very large, with a prominent keel down the middle, and is formed for the attachment of very strong muscles: the bones of the wings are analagous to those of the fore-legs in quadrupeds, but the termination is in three joints or fingers only, of which the exterior is very short. This will be better understood by the annexed: [Illustration: Skeleton of a Turkey.] The muscles that move the wings downwards, in many instances, are a sixth part of the weight of the whole body; whereas those of a man are not in proportion one hundredth part so large. The centre of gravity of their bodies is always below the insertion of their wings to prevent them falling on their backs, but near that point on which the body is, during flight, as it were, suspended. The positions assumed by the head and feet are frequently calculated to accomplish these ends, and give to the wings every assistance in continuing the progressive motion. The tail also is of great use, in regulating the rise and fall of birds and even their lateral movements. What are commonly called the legs are analogous to the hind legs in quadrupeds, and they terminate, in general, in four toes, three of which are usually directed forwards, and one backwards; but in some birds there are only two toes, in others three.