Those fringes which you see when the little doors open, are the gills. They are so red because they are filled with blood; indeed, they are made of a great number of little blood-vessels. As the fish swims along with its round mouth open, it does not swallow the water, but lets it run over its gills, and then out it comes at the little doors; the red fringes take the oxygen out of the water, and it goes into the fish's blood. The water is the fishes' atmosphere, and it is only from it that they can get air to breathe; so that if the glass globe were broken, and the pretty goldfish were let fall upon the carpet, unless they were quickly put back into water they would gasp and die from want of air; just as you would, if someone held your head long under water. So you see that the home of the fish is perfectly suited to it. In the aquarium you would observe that while most of the fishes dart hither and thither, there are some which never rise to the surface of the water. These are the flat-fish; and they keep at the bottom, because for some wise purpose God has made them without the power of rising and sinking like others. Inside most fishes there is a bag filled with air, as is the india-rubber ball which you delight to bounce so high. The fish can make this little balloon larger or smaller, just as it wishes to be itself lighter or heavier. As it swims along, it is usually about the same weight as the water; but when it wants to dive, the fish squeezes its air-bag tightly together, which causes its body to become heavier than the water--for air pressed closely together becomes heavy, and its own weight sinks it down. When it wants to rise again to the surface, it ceases to squeeze this bag, the air in the little balloon expands, and the diver rises again and floats or swims because its body is now lighter than the water. Is not this a very perfect and beautiful plan? How true it is that God has provided for the wants of all His creatures, and fitted them for the life designed for them! But besides rising or sinking when they please, fishes can turn themselves about very quickly. To understand how they do this, you must look at the long bone which runs right through the body, from head to tail. You will see that it is made, like your backbone, of a number of small bones which move upon each other so easily that they enable the fish to turn itself rapidly, as you see it does. The wonderful way in which these tiny bones are fitted together by what is called the "ball and socket arrangement" may best be seen in a large fish, such as the salmon; but a sardine's frame is made in the same beautiful way.