[Illustration: FIG. 6.--Paramœcium: _e_, mouth; _v_, contracting vacuoles.] [Illustration: FIG. 7.--Nummulites.] If the reader visits Egypt and climbs the pyramids, he will be impressed by these the greatest works of mankind. If a small portion of the stone from which they are constructed is placed under the glass, it will be found in many instances made up almost entirely of beautiful shells (Fig. 7). These are the shells of an amœba-like animal known as a Nummulite, which lived millions of years ago, and whose fossil remains formed the stone from which the early Egyptians in turn built the great piles or monuments of their kings. Man is powerful, but in this instance one of the most insignificant of animals made his work possible. These shells are of great beauty and variety (Fig. 8). Many are perforated, and through the minute holes are seen the false feet of the Amœba reaching out for food. They illustrate the boundless resources of nature, and suggest that the very lowest of creatures are not too insignificant to be dressed in most beautiful garbs, as all these forms vie with one another in the delicacy of their designs (Fig. 9) and the grace of their shapes. Some of these shelled forms are giants two inches across. All these minute shells perform a marvelous work in building up the crust of the earth, forming the bottom of deep seas and the platforms of coral reefs. The chalk cliffs of England are composed of shells of unestimated millions (Fig. 10), which were once dropped upon the bottom of a deep sea and piled upward until some were crushed into a shapeless mass of lime, others retained their shapes (Fig. 11); and all, by some convulsion, were afterward lifted high into the air. [Illustration: FIG. 8.--Flint-shelled Radiolarian.] [Illustration: FIG. 9.--Flint-shelled Polycystina.] [Illustration: FIG. 10.--Foraminifera from Atlantic ooze.] The entire ocean is as thickly populated with these atoms as the drop of fresh water. The shelled forms are as constantly dying, the shells falling or sinking in a continual rain of shells upon the bottom, piling up eternally. Who shall estimate their countless numbers? It is believed that these minute shells are as abundant down to a depth of six hundred feet as they are at the surface. There are more than sixteen tons of limy shells floating in the uppermost one hundred fathoms of every square mile of the ocean. These facts convey an idea of one way in which the earth is growing--increasing in size but not in weight, as these delicate creatures merely secrete the carbonate of lime which forms their shells. They take it from the surrounding water of which it has been a part. [Illustration: FIG. 11.--Section of English chalk cliff. Highly magnified. Bottom of an ancient sea.]