18 ZOOLOGY. 



of blood ; but no one anticipated this discoloration (which was regarded as a 

 mark of divine 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 arc sometimes so abundant as to form entire 

 o;eological 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 oi 

 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 yery 

 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 mhrilla^ 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 vibrillse 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, whence the name of rotifera. 



The BaccilarioB (now regarded as plants) are united together side by 

 side in ribbon-like bands. B.paradoxa is a very interesting species, which 

 may be compared to a ruler ; but as many individuals rest side by side like 

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