Very familiar examples of this structure may be found in the many creatures which inhabit the waters and breathe by means of gills, which extract the oxygen of the water. Take, for example, a Lobster or a Crab, open it, and look at the white, pointed, uneatable objects which are popularly called “ladies’ fingers.” These are the gills, or breathing apparatus, and their structure is really wonderful. They are composed of innumerable laminæ, or very thin plates, covered with an exceedingly fine membrane, and placed closely side by side, but with sufficient distance between them to allow the water to percolate the whole structure. With the aid of an ordinary pocket lens the observer may make out a most wonderful system of blood-vessels, which permeate every one of the myriad laminæ, and which extract the life-giving oxygen from the water as it passes between them. Then, to pass to animals of a higher order, take the gills of fishes. Any fish will do, provided that it be fresh, and, if it can be examined immediately after death, so much the better. Taking things reciprocally, the gills of the fish and the laminæ of the stove, are identical in principle, namely, the exposure of much surface with little loss of space. If possible, the observer should inject the blood-vessels of the gills with the conventional crimson and blue wax, showing the currents of the arterial and venous blood. Each lamina forms a most wondrous object, and may be gazed upon for weeks with increasing admiration. Every one who has watched the habits of fishes must have noticed that in running waters they always have their heads against the stream, and do not greatly care about shifting their positions. In still waters, especially such as those of the ordinary glass aquaria, the fish are perpetually on the move, whereas in such a river as the Dove of Derbyshire, and even the Darenth of Kent, large trout may be seen almost motionless, but invariably with their heads directed up the stream. The reason is evident enough. As long as the fish lies with its head up the stream the water flows through its gills, and enables it to breathe. Were the passage of the water stopped, the fish would be drowned. Consequently, all good anglers, when they hook a fish which is worth taking, keep its head down the stream, prevent the water from washing over its gills, and consequently render it so weak by deprivation of oxygen, that it becomes an easy prey, and is rendered subservient to a line of a single hair. Let the fish breathe, and a single struggle would smash a line of treble the strength. But keep it from breathing by directing its head down the stream, and it rapidly loses all strength, and can be directed into the landing-net, or brought within the scope of the gaff, without a chance of escape. * * * * *