than that of a whale; and one of the last conclusions at
which we arrive, is a conviction that the greatest and most
probable explanation, and the case of Infusoria no longer appears to differ from that of other animals as to the principle on which their propagation is conducted. The chief peculiarity seems to consist in this, that their increase takes place both by the oviparous and viviparous manner of descent from parent animals, and also by division of the bodies of individuals.
The great difficulty is, to explain the manner in which the eggs or bodies of preceding individuals can find access to each particular infusion. This explanation is facilitated by the analogous cases of various fungi which start into life, without any apparent cause, wherever decaying vegetable matter is exposed to certain conditions of temperature, humidity, and medium. Fries explains the sudden production of these plants, by supposing the light and almost invisible sporules of preceding plants, of which he has counted above 10,000,000 in a single individual, to be continually floating in the air, and falling every where. The greater part of these never germinate, from not falling on a proper matrix; those which find such matrix start rapidly into life, and begin to propagate.
A similar explanation seems applicable to the case of Infusoria; the extreme minuteness of the eggs and bodies of these animalcules probably allows them to float in the air, like the invisible sporules of fungi; they may be raised from the surface of fluids by various causes of attraction, perhaps even by evaporation. From every pond or ditch that dries up in summer, these desiccated eggs and bodies may be raised by every gust of wind, and dissipated through the atmosphere like smoke, ready to start into life whenever they fall into any medium admitting of their suscitation; Ehrenberg has found them in fog, in rain, and snow.
If the great aerial ocean which surrounds the earth be thus charged with the rudiments of life, floating continually amidst the atoms of dust we see twinkling in a sunbeam, and ever ready to return to life as soon as they find a matrix adapted to their development, we have in these conditions of the very air we breathe a system of provisions for the almost infinite dissemination of life throughout the fluids of the present Earth; and these provisions are in harmony with the crowded condition of the waters of the ancient world, which is manifested by the multitudes of fossil microscopic remains, to which we have before alluded. (See Sect. viii. page 290.)
Mr. Lonsdale has recently discovered that the Chalk at Brighton, Gravesend, and near Cambridge, is crowded with microscopic shells; thousands of these may be extracted from a small lump, by scrubbing it with a nail brush in water; among these he has recognised vast numbers
