INFUSORIA. 91° 
The modes of locomotion in the Infusoria are various. Some swim by 
means of the vibrilla; some, like the monads, revolve like a globe on its 
axis; others roll upon their transverse axis; others glide along with a regu- 
lar motion like the snails; and others like the leech. 
The reproduction of the Infusoria takes place by means of spontaneous 
division; by budding, which is the least common; and perhaps by the 
ordinary mode of generation, although this is denied by Dujardin, who 
affirms that there are no males; and indeed, no indications of sexual instinct 
have been observed among them. The first mode of reproduction occurs 
in the so-called Polygastrica, and takes place either transversely or longi- 
tudinally, each half forming an independent animal. The division is not 
always complete, and in this case the two parts remain attached to each 
other. Some present a singular peculiarity, in which the soft part alone of 
the animal is divided, whilst the harder parts or armor remain undivided, 
as in Ophrydium versatile, which often divides itself to the extent of mil- 
lions, whilst the gelatinous exterior remains entire, although it increases in 
size. In others the protection is completely divided, whilst the animals 
remain more or less closely united. The division in pedunculated genera 
does not generally extend beyond the pedicle, which, in case the divisions 
are numerous, resembles the trunk of a small tree. This remarkable mode 
of reproduction by division proceeds with such rapidity under favorable 
circumstances, that a single animal may give rise to a million of descend- 
ants in the course of eight or ten days. 
The sudden and unaccountable appearance of Infusoria, especially in 
closed vessels, was once attributed to spontaneous or equivocal generation, 
a theory which still has its defenders, although it appears to be pretty well 
ascertained that.such a hypothesis is not necessary. We may readily 
imagine that the inconceivably minute eggs of such creatures (or of those 
of which these animalcula are the imperfect condition) can be raised into 
the air with vapor and transported in all directions, penetrating wherever 
the air itself finds access. 
The vital power of some species (and of the crustaceous Rotifera) is so 
great that they can survive with so little moisture as to be considered dry, 
exhibiting no signs of vitality until moistened with a drop of water, when 
they resume their active life. Doyére found that they may be completely 
dried in sand, in the dry air, or in a vacuum, and be revived by placing 
them in water. When placed in water at the temperature of 50° Centigrade 
(=126° F.) they were killed, but would revive if the temperature did nof 
exceed 45° or 48° Cent. Some species are said to occur naturally in warm 
springs whose temperature equals 40° or 50° Cent.; whilst some species are 
not destroyed by being frozen. Ehrenberg found Infusoria in materials 
taken from floating masses of ice, and in sea water from a depth of 1100 to 
1600 feet, brought by Captain Ross from the regions towards the south pole, 
between the latitude of 63° and 78°, where the temperature must have been 
very low, and the light much reduced at such a depth. 
The extent of certain geological strata made up of the solid parts of the 
Infusoria is extraordinary, when the minuteness of the aggregated particles 
ICONOGRAPHIC ENCYCLOP£DIA,—VOL. II. 15 225 
