18 ZOOLOGY. 
of blood; but no one anticipated this discoloration (which was regarded as a 
mark of eee displeasure) to be due to animals. 
Leeuwenhoek, in 1675, first observed the infusoria, in standing rain water, 
without being fully convinced of their animal nature. Subsequently, in 
pursuing some medical inquiries into the nature of the material which gives 
its pungency to pepper, he made an infusion of this substance, which he was 
afterwards astonished to find swarming with animals. They were subse- 
quently found in infusions of other vegetables, and in those of animal and 
metallic substances; and although it has been found that infusions are not 
essential to their production, they still retain the name of Infusoria. They 
are also called Protozoa, because they were supposed to constitute the first 
appearance of animal life. In the year 1701, Leeuwenhoek discovered that 
Rotifera, from the sediment which had been dried for a year in the gutter 
of a roof, could be revived. From this date, notwithstanding the number 
of observers, no one seemed disposed to investigate the internal structure 
of these minute objects, until the researches of Ehrenberg showed that they 
are provided with at least a mouth and a digestive cavity. 
The larger species of Infusoria attain the size of a tenth of a line or more. 
The body is gelatinous and naked, but some are protected by a coriaceous, 
calcareous, or silicious defence; and as these mineral materials remain after 
the death of the animal, they are sometimes so abundant as to form entire — 
geological formations. Some Infusoria have the body covered with minute 
sandy particles; others have only a shield upon the back; others again 
-have the entire body inclosed in a case with one or more openings. When 
a defence is present, it is usually in a single piece, although there are some 
composed of more. 
The Infusoria are usually colorless and translucent, but some are green, 
some yellow, and a few red; and when these colored species are very 
abundant, they give the water a discolored appearance. The shape is 
globular, oval, fusiform, cylindrical, vermiform, or irregular; and some are 
continually varying their form, so that the same individual might be mis- 
taken for several distinct species. This is especially the case in the genus 
Proteus, which has derived its name from the sudden and great variation of 
form the same individual assumes under the eye of the observer. A head, 
neck, and tail, are usually distinguishable, and in some one end is very 
long, giving the animal a fanciful resemblance to a swan. The tail is 
sometimes used as a foot, and in some species is capable of being extended 
like the tube of a telescope. There are various external appendages like 
spines or bristles, but the most usual of these are the vibralle, which are 
used in locomotion, and to draw the food within reach by forming a kind 
of minute whirlpool in the water. In the Rotifera (which are really 
Crustacea) the vibrillee are arranged in two circles at the anterior extremity ; 
and when they are in action, some observers fancy that they resemble 
wheels in a state of rotation, Sea the name of rotifera. 
The Baccilarie (now regarded as plants) are united together side by 
side in ribbon-like bands. 4. paradowa is a very interesting species, which 
may be compared to a ruler; but as many individuals rest side by side like 
222 
