. The microscope; a simple handbook. Microscopes. Fig. 117.âForaminifera. The Foraminifera are from a structural point of view similar to the Heliozoa, being morsels of jeUy having the power of forming round themselves shells of chalk extracted from their food and the water in which they live. These shells take myriads of different forms, but have one thing in com- mon : they are perforated with multitudinous holes through which slender threads of jelly exude. To this family belong the shells which form chalk. Innumerable numbers of these tiny creatures fall, as they die, to the bottom of the
. The microscope; a simple handbook. Microscopes. Fig. 117.âForaminifera. The Foraminifera are from a structural point of view similar to the Heliozoa, being morsels of jeUy having the power of forming round themselves shells of chalk extracted from their food and the water in which they live. These shells take myriads of different forms, but have one thing in com- mon : they are perforated with multitudinous holes through which slender threads of jelly exude. To this family belong the shells which form chalk. Innumerable numbers of these tiny creatures fall, as they die, to the bottom of the ocean, forming there, in the course of ages, a layer of chalk which may later be raised by volcanic action above the sea-level. Such examples illustrate the gradual development of a shell, the creature in every other respect retaining its original simplicity. We can now trace â development in a difierent direction leading to more complex creatures endowed with locomotion. The jeUy or protoplasm of which the living animal is formed appears to slightly harden all round its borders, and a creature of a more or less definite shape is produced, still very elastic and capable of retracting or extending itself to per- haps three times its normal length. It has a somewhat pointed end, and the margin of its body is stiU sufficiently soft to enable it to Trypano- feed by absorbing into its substance through any some, portion of the surface small particles of food, but it cannot get outside such large things as the Amoeba. This is the creature which, if it finds its way into the blood of animals or men, causes in one case the tzetze-fiy disease and in the other the dread sleeping-sickness, and it is known as the Trypan osome. A further stage shows the de- velopment of a flagellum, or whip, which is formed by the drying up and hardening of the pointed end of the body. The flagellum vibrates, and by its aid the creature can swim about with considerable rapidity. In- numerable for
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