INFUSORIA. 21 



The modes of locomotion in the Infusoria are various. Some swim by 

 means of the vibrilhe ; 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 (^f spontaneous 

 division ; by budding, which is the least common ; and perhaps by the 

 ordinary mode of generation, although this is denied by Dujardin, who 

 atfirms 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 OjpJirydium 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, althougli 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 w^hich 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. Doyere 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 not 

 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 material 

 taken from floating masses of ice, and in sea water from a depth of 1100 ti> 

 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 



ICONOGRAI'HIC ENCYCLOP/EDIA. VOL. II. 15 225 



