INFUSORIA. 
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rulers upon a table, they may form a square or parallelogram. _ || il] 
The motion is peculiar, each single body (the edges remaining in | i 
a line) being capable of sliding rapidly along the one with which | 
it is in contact; so that when those upon one side have extended ! 
themselves, the whole may resemble a flag attached to a pole, as | 
in the diagram. | 
The Gaillonelle (plants) are united end to end, forming a ) 
chain. In the genus MMeridion the individual parts or frustules are 
wedge-shaped, so that when placed edge to edge they form an arch, or even 
a circle or spiral. In Jficrastercas the interior is divided into many cells. 
Tsthmia has an end fixed, and forms rows, the parts being in contact at 
different angles by a small isthmus. 
All the animal Infusoria seem to be provided with a mouth, which is 
generally terminal, but sometimes placed near the middle of the body. The 
vent is not always present, or at least has not been discovered in all, so that 
it is possible that the undigested portion of the food may be rejected from 
the mouth, as in the Polypi. Where it has been observed, the vent was 
near the mouth; or upon the abdomen; or at the posterior extremity. 
above or below. The breathing organs, where they have been observed, 
appear as simple openings. The organs of motion are the tail, foot, bristles, 
vibrille, &e. 
The organs of sense, as far as known, are those of feeling (of which the 
snout, and perhaps the bristles, are the organs), and perhaps vision, although 
Dujardin doubts the existence of the latter. The organs supposed to be 
eyes are dark red or black stigmas situated anteriorly upon the upper side, 
and Ehrenberg thinks that a glandular body beneath them performs the 
function of an optic nerve. Most of the polygastrica have a single stigma, 
Distigma has two; some of the Rotifera (crustacea) two, three, four, or 
more, arranged in two clusters, as in Zheorus; in a semicircle, as in 
Cyclogena ; or upon pedicles (like those of land snails) as in Oéoglena. It 
is uncertain whether the structure of these eye-like spots resembles that of 
any of the animals above them; or whether their vision, if they possess 
this sense, is more than sufficient to distinguish light from darkness. Indeed, 
a perfect vision would scarcely be of much use to them, as they are said 
not to sleep, but to be as active in darkness as in light. 
The internal organization of these singular animals is not less interesting 
than their exterior form; and indeed it may be considered the more sur- 
prising, when their size, in comparison with that of the larger animals, is 
taken into consideration. Their movements are extremely multifarious, 
_and for all these there is an appropriate system of muscles. These may be 
observed running in various directions, the most interesting being those 
which keep up the unceasing play of the vibrille. But these organs are 
not confined to this class, vibrillee being found externally and internally in 
many. of the higher animals. 
In the Polygastrica Ehrenberg represents a long curved intestine with 
numerous globular bodies suspended to it somewhat like grapes, from the 
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