CHAPTER XXVI. 



OF THE PROTOZOA. 



1106. THIS, the lowest division of the Animal Kingdom, in- 

 cludes a multitude of minute creatures, of an exceedingly simple 

 structure, in which no traces of many of the organs which we 

 are accustomed to see in an animal can be detected even with 

 the highest powers of our microscopes. Ehrenberg, indeed, at- 

 tributed a very considerable complexity of organisation to them, 

 but the researches of subsequent observers have shown that in 

 many cases the learned Professor of Berlin was in error ; and 

 most of the Naturalists of the present day have been inclined to 

 regard them as consisting, like the lowest plants, of simple cells 

 endowed with an independent vitality. It is, however, difficult 

 to understand how all the properties possessed by these creatures 

 should really appertain to a simple cell, and of late there 

 has been a tendency to doubt their unicellular nature. The con- 

 sideration of these views will, however, be best left until we 

 come to treat of the Infusoria, the most highly organised group 

 of the Protozoa. 



1197. It may be stated, however, that the gelatinous mass of 

 which the Protozoa are composed, which has been denominated 

 sarcode by M. Dujardin, exhibits small vacant spaces in differ- 

 ent parts of its substance ; these are called vacuoles, and were 

 taken for empty stomachs, by Ehrenberg and other observers. 

 Imbedded in their walls there is always a dark body called the 

 nucleus, and one or more clear pulsating spaces, or contractile 

 vesicles, which appear in many cases to be connected with a 

 system of vessels serving for the circulation of fluids. Many 

 possess a mouth and oesophagus, but there is no distinct alimentary 

 canal, although the foecal matters are frequently discharged from 



