The Revolving Volvox, V. globator (Figs. 34 and 35), is found in great abundance, during summer, in tanks and ponds of stagnant water. It consists of green or brownish-yellow globules about the eighth part of an inch, formed of animalcules scattered round a gelatinous and diaphanous spherical membrane, each furnished with a flagelliform filament and with a reddish interior point, which Ehrenberg took for an eye. Leuwenhoek first observed this Volvox in marshy waters. This eminent naturalist has left a very interesting account of his observations on these microscopic inhabitants of the waters, displaying an amount of patience and address which cannot be too much admired; his observations were made with a simple lens, which he constructed himself. In one hand he held his instrument, which was very coarse if we compare it to the more perfect and infinitely more powerful instruments now in use; whilst, in the other hand, he carried to his eye the glass tube full of water which contained the object under observation. "The microscopes of Leuwenhoek," says Dujardin, "were the very smallest bi-convex lenses, mounted in a silver frame. He made a collection of twenty-six, which he bequeathed to the Royal Society of London. These instruments, subject to all the inconveniences of a maximum of spherical aberration and a total want of stability, were only fit for use in the hands of Leuwenhoek himself, who had acquired, in his labour of twenty years, habits of observation which compensated, in great part, for the want of perfection in his instruments."
The Eugleniæ are infusoria usually coloured green or red. Their form is very variable. They are oblong or fusiform in shape, swelling at the middle during action, and contracted or bowl-shaped in repose, or after death. They are furnished with the usual whip-shaped filament, which issues from an opening in front, and from one or many reddish points irregularly placed anteriorly.
Euglenia viridis (Fig. 36) is the most common species, and, perhaps, the most widely diffused of all the Infusoria. It is this animalcule which habitually covers stagnant pools with its floating surface of green, and which forms, on the surface of marshy waters, the shining pellicle so strongly coloured, which, collected upon paper, so long preserves its brilliant tint.
Fig. 86. Euglenia viridis (Ehr.), magnified 350 times.
The Euglenia sanguinea, at first green, becomes subsequently of a blood colour. It has often been met with by microscopists. Ehrenberg, who first described it, attributes to its great abundance the red colour of some stagnant waters. Its presence explains the pretended miracle of water changing into blood, which was frequently invoked by the Egyptian priests.
Ciliate Infusoria.
Fig. 37. Cothurnia pyxidiformis
(Udckem).
Let us now take a glance at some of the more remarkable species of Ciliate Infusoria. The bodies of these creatures are all more or less translucent. They have not substance enough, in fact, to reach a state of opacity. Their bodies are more or less globular or ovoid, sometimes fashioned like a shuttle, or curved while growing, sometimes swollen in the middle like an ampulla, or bell-shaped, and flattened into a discoid shape; some slightly resemble a tadpole, a thimble, a shoe, a rose-bud, a flower, even a seed.