The science of life : fully illustrated in tone and line and including many diagrams

BOOK 2

radiolaria, for example, is the presence in their bodies of tiny globular ‘“ yellowcells.” ‘These cells are alge, entangled and held in the protoplasm of the radiolarian ; they can survive the death of their host and live and multiply independently. Here, again, the radiolarian benefits by the synthetic powers of the alge, and the alge benefit by being protected. There are similar organisms in other protozoa, and even in the tissues of certain many-celled animals. Some species of the common fresh-water polyp Hydra (Chapter 4, § 3) are coloured a brilliant green by plantcells in their tissues, and nearly all corals have yellowish alge in the inner layers of their bodies and apparently cannot live

Fig. 117.

without them. And there are flat-worms and sponges which do the same thing.

This relationship provides an amusing armchair speculation. Should the alge in a radiolarian, say, be called part of the organism or not? Pro: They are apparently indispensable to the organism, an integral part of his body. Con.: They can survive his death and lead happy, active lives of their own. The triplex author leaves this nice question unanswered ; he states the facts and leaves the interpretation to his reader.

§ 6 Slime-moulds We come now to an exceedingly curious

group of creatures lying on the broad frontier between the animal and vegetable

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THE SCIENCE OF LIFE

The birth of a Lichen—fungus-threads, which have just grown out of spores (Fig. 116), are surrounding and capturing globular alge (highly magnified).

CHAPTER 6

kingdoms—a group of creatures of no importance whatever to the practical man, but of the utmost philosophical and scientific interest, common enough, sometimes even conspicuous, and yet hardly ever noticed except by naturalists.

For most of its life a slime-mould (the technical name of the group is either Myxomycetes, meaning slime-fungi, or Mycetozoa, meaning fungus-animals) is a naked, slimy mass of protoplasm, an almost formless mass without cells or special tissues. Its appearance varies from species to species. It may be translucent, or white, or pink, or green, or yellow, or purple ; it is usually large enough to be easily seen, and in extreme cases such as the bright yellow “ flowers of tan’ it may be as much as a foot square and two inches thick—one can fill a bucket with this formless creature. It-is found in such situations as decaying logs, old tree-stumps, heaps of rotting dead leaves, and the like. Usually it is spread out as a thin creeping film of living substance without enduring shape. It is nearly as structureless as a dropped egg. To the naked eye it presents a veined pattern, having a network of thickened strands connected together by thin films in the meshes. Seen through the microscope, it is a simple sheet of protoplasm without nerves or muscles or digestive organs or any such specialized parts—not even divided up into cells. It is dotted with thousands of nuclei and contractile vacuoles; the protoplasm consists, like the protoplasm of an amoeba, of a clear outer layer and granular inner mass. ‘The creature is, in fact, like a gigantic amoeba.

The substance of this plasmodium, as the large, creeping stage in the life-history of a slime-mould is called, is in continual sluggish motion. It ebbs slowly hither and thither, often with a regular rhythmic motion, flowing in one direction for a minute or two and then reversing. Generally the streams in one direction are longer and stronger than those in others, and so the mass of thin fluid jelly surges along. Its motion is so slow as to be barely perceptible ; nevertheless, it creeps with an appearance of appetite and purpose. Normally (unless it is about to form spores) it avoids light and makes its way into damp, dark corners. At its advancing fringe it puts out and withdraws lobes, like the lobes of an ameceba,