But this digression is becoming humiliating, and meanwhile our hands are getting benumbed with cold. In spite of that, I hold the jar up to the light, and make a background of my forefingers, to throw into relief some of the transparent animals. Look at those light green crystal spheres sailing along with slow revolving motion, like planets revolving through space, except that their orbits are more eccentric. Each of these spheres is a Volvox globator. Under the microscope it looks like a crystalline sphere, studded with bright green specs, from each of which arise two cilia (hairs), serving as oars to row the animal through the water. The specs are united by a 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,[20] 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.[21]
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,”[22] 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 not unfrequently exhibit a somewhat similar metempsychosis, and make up for the fitful capriciousness of wandering youth, by the steady severity of their application to business, when width of waistcoat and smoothness of cranium suggest a sense of their responsibilities.
Whether this loss of locomotion is to be regarded as a retrogression on the part of the plant, or animal, which becomes fixed, may be questioned; but there are curious indications of positive retrogression from a higher standard in the metamorphoses of some animals. Thus the beautiful marine worm, Terebella, which secretes a tube for itself, and lives in it, fixed to the rock, or oyster-shell, has in early life a distinct head, eyes, and feelers; but in growing to maturity, it loses all trace of head, eyes, and even of feelers, unless the beautiful tuft of streaming threads which it waves in the water be considered as replacing the feelers. There are the Barnacles, too, which in the first stage of their existence have three pairs of legs, a very simple single eye, and a mouth furnished with a proboscis. In the second stage they have six pairs of legs, two compound eyes, complex in structure, two feelers, but no mouth. In the third, or final stage, their legs are transformed into prehensile organs, they have recovered a mouth, but have lost their feelers, and their two complex eyes are degraded to a single and very simple eye-spot.
Fig. 12.
Water Beetle and its larva.
But to break up these digressions, let us try a sweep with our net. We skim it along the surface, and draw up a quantity of duckweed, dead leaves, bits of stick, and masses of green thread, of great fineness, called Conferva by botanists. The water runs away, and we turn over the mass. Here is a fine water-beetle, Dytiscus, and a larva of the same beetle, called the “Water-tiger,” from its ferocity ([Fig. 12]). You would hardly suspect that the slim, big-headed, long-tailed Water-tiger would grow into the squat, small-headed, tailless beetle: nor would you imagine that this Water-tiger would be so “high fantastical” as to breathe by his tail. Yet he does both, as you will find if you watch him in your aquarium.
Fig. 13.