So few people know the turtle's egg that it will be better to describe that of the hen, which it largely resembles. Underneath the hard shell is a tough but flexible membrane which lies against the limey coating, except at the blunt end, where a separation between the two gives room for a bubble of air. Inside of this shell and its membrane lies the white of the egg, which is nourishment for the chick, though not nearly so rich as the yolk. This, besides the albumen which it contains, is stored with large quantities of fat. It will be remembered that upon breaking a hen's egg and dropping it into a bowl, the yolk holds together because it is enclosed in a delicate sac. As the yolk falls into the bowl there floats to the top of it a lighter yellow spot as big as the end of a lead pencil. This is all of the egg which thus far represents the chick itself. All the rest is nourishment. This disk already consists of three reasonably distinguishable layers of cells, which grow rapidly different from each other. They spread and bend and twist, forming the young chick and a set of organs which serve for its protection and maintenance during its embryonic life. Within a few days these accessory organs will have formed distinctly. Within the upper half of the yolk will be found the small developing chick, which for the first thirty-six hours of its development passes through a stage not unlike the fish, or the earlier steps of the turtle. Within a few days it becomes clearly evident that this creature is to be a bird, though it is much longer before it is clearly a chick. This embryo is so soft that it is almost like curd in thickened milk, and could be very easily destroyed were it not for a protective device which Nature has employed. It seems necessary that it should be protected with the utmost care. The matter will be better understood if we recall a common experience. Almost everyone has tried to dissolve some substance in water in a vial. If the bottle be filled with fluid to the top and corked it is very difficult to shake up the contents. Even vigorous agitation produces little movement of the material on the inside. If we wish to shake up the solid with water the bottle must be left partly empty. The brain of a human being is protected by just the same device. If it simply lay within the skull the first fall would mash the gray substance against the side of the cavity. To prevent this calamity the bony case is made somewhat larger in capacity than the brain itself, and the space between the two is filled with a watery fluid. This serves to prevent jars and shocks. In the hen's egg the same plan is pursued. The embryo lies on the inside of a bag considerably larger than itself. This sac, called the amnion, is filled with a watery fluid. With such a protection only the most severe shock to the egg would sufficiently jar the embryo to do it any harm. The ordinary experiences of an egg leave it undisturbed.