354 



NATURAL HISTORY. 



going along more slowly, either steadily or turning over from side to side, and screwing 

 themseh 7 es, as it were, forwards. Sometimes a dozen or more will come within the range of 

 vision, and twist and turn in every direction, and suddenly rush oft', moving so as not to come 

 in collision. Occasionally a globular-shaped thing will come by and stop, and just as suddenly 

 will leap, as it were, in the water, and go right out of sight. Now and then a great current of 

 water appears to be in motion, near the side of the field of vision, and if the slide holding the 

 water be moved, so as to bring it beneath the eye, some balls, like specks, are seen united to 

 delicate stems. They produce much movement in the water, and are suddenly dragged back- 

 wards towards their fixed point. Here and there, settled down and resting on a kind of stem, 

 some pear-shaped things may be seen, with delicate hairs sticking out from their ends. A still higher 

 power of the microscope, which will magnify from 300 to 1,000 times, enables other and smaller 

 creatures to be seen, and renders the minute structures, of the larger, visible and capable of study. 

 Amongst the smaller ones are little bag- shaped things, with one or two hair-like projections the cilia 



which keep them in movement and in places here and 

 there are multitudes of little moving things, mere 

 lines of matter, with an end produced into a hair-like 

 tail or flagellum. These are amongst the simplest of 

 living things, and may be animal or may belong to 

 the lowest plants. The microscope reveals, amongst the 

 larger kinds x . that they move in consequence of the 

 vibration, or to-and-fro movement of microscopic cilia, 

 and that the kinds which are stalked can be retracted 

 by the contraction of a granular tissue resembling the 

 simplest form of muscle. 



If lately-collected rain-water is examined in the hope 

 of discovering any of these miimte forms of life, disap- 

 pointment will occur. But if some hay, or any vegetable 

 matter, be allowed to soak in pure water exposed to the 

 air, or if pieces of flesh, brain, blood, or any animal 

 substance, be placed in water, and also exposed for a 

 day or two, a great many species of these aiiimalcules, or Infusoria, the individuals being in 

 vast multitudes, will be distinguishable. Certain kinds of these animalcules are almost 

 invariably to be found in water in which particular vegetable or animal substances have been 

 soaked, and a succession of kinds is often observed to occur as the infusion gets old. The free 

 access of air is requisite for all this, and the hay and animal substances form the food of the minute 

 creatures, whose derivation is not from the minute structures or broken-down tissues of the plant 

 or animal. The air contains the extremely minute spores, or reproductive particles, whence the 

 animalcules spring. There is no spontaneous generation of these animalcules, and no turning of dead 

 animal or vegetable tissue into them. The term Infusoria, or animals of infusion, merely relates to 

 where they are to be found in most instances, but not invariably, and it must be carefully noted that 

 the animalcules are not derived from the infusions. Certain infusions suit particular kinds of 

 Infusoria, and these particular species are to be found in them. 



The Infusoria are exceedingly simple in their construction, may be said to be uni-cellular, and 

 are allied, as Protozoa, to the Rhizopoda. There is this distinction, however, that whilst the majority 

 of the Infusoria move actively, and a great number are sedentary, or move during some part of their 

 life-cycle, they rarely have silicious or calcareous tests,* and the pseuclopodia, which sometimes exist, 

 never run together as they do in Gromia and Amoeba amongst the Rhizopoda. The body is usually 

 soft, and there are one or more contractile vesicles. A nucleus exists, and there are vacuoles which 

 contain food. The outside of the body is ciliated in a great number, has but one or two long cilia in 

 front in others, and one group has no cilia, but tubular processes project from the more or less 

 pear-shaped body, and really act as suckers. 



The following are examples of the four great divisions or orders of the Infusoria. 



* Haeckel has described some with tests. 



Fig. 2. PAHAMECIUM AURELIA. 



4, Lateral, n, ventral surface ; c, in conjugation ; cv, contractile 

 vesicle, n, nucleus; b, oral aperture. 



