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 delicate network, which is not always visible, however. Inside this sphere is a fluid, in which several dark-green smaller spheres are seen revolving, as the parent-sphere revolved in the water. Press this Volvox gently under your compressorium, or between the two pieces of glass, and you will see these internal spheres, when duly magnified, disclose themselves as identical with their parent; and inside them, smaller Volvoces are seen. This is one of the many illustrations of Life within Life, of which something was said in the last chapter.

Nor is this all. Those bright green specs which stud the surface, if examined with high powers, will turn out to be not specs, but animals, and as Ehrenberg believes (though the belief is little shared), highly organized animals, possessing a mouth, many stomachs, and an eye. It is right to add that not only are microscopists at variance with Ehrenberg on the supposed organization of these specs, but the majority deny that the Volvox itself is an animal. Von Siebold in Germany, and Professor George Busk and Professor Williamson in England, have argued with so much force against the animal nature of the Volvox, which they call a plant, that in most modern works you will find this opinion adopted. But the latest of the eminent authorities on the subject of Infusoria, in his magnificent work just published, returns to the old idea that the Volvox is an animal after all, although of very simple organization.

The dispute may perhaps excite your surprise. You are perplexed at the idea of a plant (if plant it be) moving about, swimming with all the vigour and dexterity of an animal, and swimming by means of animal organs, the cilia. But this difficulty is one of our own creation. We first employ the word Plant to designate a vast group of objects which have no powers of locomotion, and then ask, with triumph, How can a plant move? But we have only to enlarge our knowledge of plant-life to see that locomotion is not absolutely excluded from it; for many of the simpler plants—Confervæ and Algæ:—can, and do, move spontaneously in the early stages of their existence: they escape from their parents as free swimming rovers, and do not settle into solid and sober respectability till later in life. In their roving condition they are called, improperly enough, "zoospores," and once gave rise to the opinion that they were animals in infancy, and became degraded into plants as their growth went on. But locomotion is no true mark of animal-nature, neither is fixture to one spot the true mark of plant-nature. Many animals (Polypes, Polyzoa, Barnacles, Mussels, &c.), after passing a vagabond youth, "settle" once and for ever in maturer age, and then become as fixed as plants. Nay, human animals