100 THE OCEAN WOKLD. 



are found in the liquid excrements and other products of certain 

 organisms, and they have heen noted even in women's milk. 



But, as their name indicates, it is in aqueous infusions, vegetable or 

 animal, that these animalcules abound. Armed with a microscope, the 

 reader may, with very little trouble, afford himself the pleasure of 

 studying these animals. It is only necessary to place some organic 

 debris the white of an egg, or some grass, for example in a vase 

 with a large mouth, filled with water, and expose it to the light and 

 air. Certain reagents, as phosphate of soda, the phosphates, nitrates, 

 or oxalates of ammonia, or carbonate of soda added to these infu- 

 sions, will singularly favour the development of Infusoria. 



There are also some accidental infusions which seem to furnish 

 these microscopic beings in great abundance. Water which stagnates 

 in garden soil or in vegetable mould, in the watering-cart or in 

 flower vases, is filled with myriads of these beings. 



So much for the medium in which they live, move, and have their 

 being. Let us pass on to their organization. We have already dwelt 

 on their extreme minuteness; their mean size is a fifth of a line 

 or the sixtieth part of an inch ; the largest species scarcely reveal 

 themselves to the naked eye. They are generally colourless ; some of 

 them are, nevertheless, green, blue, red, brown, and even blackish. Seen 

 on the object-glass of the microscope, they appear to be gelatinous, trans- 

 parent, and naked, or invested with an envelope more or less resistant, 

 which we shall designate after Dujardin by the term Sarcoda, a sub- 

 stance which is homogeneous, diaphanous, elastic, contractile, and, above 

 all, destitute of every kind of organization. They are usually ovoid or 

 globular. Those most frequently met with, and which attract the 

 most attention from observers, are. furnished with vibratile cilia, 

 which cover the whole body, acting as paddles. These organs are 

 evidently intended to propel the animal from one place to another. 

 At other times they appear to be employed in conveying food to the 

 mouth, if we may use the expression. Some Infusoria are without 

 these cilia, having only one or many very slender filaments, the 

 undulating movement of which suffices to determine their progression 

 through the liquid which surrounds them. 



Authors who have written on the Infusoria have sometimes, like 

 Leuwenhoek, Ehrenberg, and Pouchet, attributed to them a very com- 



