690 PROTOZOA. 



(with the intestines apparent,) and 2. ANENTERA, (without intes- 

 tines,) each legion including both naked and coated species. 



These Polygastrica seem to be universally diffused, one set of 

 forms inhabiting salt water, another fresh. Every mineral fount 

 has its peculiar inhabitant. They are found with the red snow 

 of the Alps and the poles, and in the waters of hot springs. In 

 a word, wherever organic matter exists in a decomposing state, 

 there they abound, " acting as scavengers in devouring in the state 

 of comminution and decay, those particles of decomposing veg- 

 etable matter, which, if left to be diffused throughout the atmos- 

 phere, might be productive of the most pernicious malaria." 



Of the Enterodela an example is had in Bursaria truncateHa. 

 This is found in ditch water, and is so large as to be seen by the 

 naked eye, resembling an egg in shape, with one end deeply hol- 

 lowed ; and from one-fourth to one-third of a line long. (N. B. 

 The line employed in Natural History is the twelfth part of a 

 French inch.) Of the Anentera we name of the genus Monas, 

 the species M. crepuscidum, the TWILIGHT MONAD, one of 

 the most minute and most simple of all the living beings made 

 known by the most powerful microscopes, resembling a mere 

 ciliated cell, and in size only the twelve thousandth part of an 

 inch. If a few stalks of hay be tied together and suspended in 

 a jar of water, the contents remaining untouched, the second day 

 after, there will appear a sort of scum on the surface of the 

 water, that has become turbid and slightly tinged with green. 

 When a minute drop of this liquid is examined with a micro- 

 scope having a magnifying power of about two hundred diame- 

 ters, the water is found' to swarm with immense multitudes of 

 minute round or oval atoms, which move rapidly with a gliding 

 action. These are MONADS. 



All infusions of vegetable and animal substances are found to 

 be speedily filled with animals resembling these or others of the 

 genus Vibrio, the latter bearing some likeness to an eel, (now 

 placed among the Intestinal Worms-) Upon these minute crea- 

 tures strong poisons seem to have no immediate effect, though a 

 few drops of alcohol suffice to strike dead the five millions of 

 living beings found in a barrel of vinegar. 



All the Infusoria seem to be provided with a mouth, generally 

 terminal, but sometimes placed near the middle of the body. The 

 breathing organs, so far as known, are simple openings. The 

 sense of feeling perhaps has its appropriate organs in the mouth 

 and the vibratile cilia by which it is surrounded. The eyes are 

 supposed to be the dark red or black stigmas which the micro- 

 scope reveals as situated in front, on the upper side. Most of 



