THE NATURE OF REPRODUCTION. 



577 



II. Infusoria. These are microscopic organisms, first discovered by 

 Leeuwenhoek, in 1675, in rain-water which had been kept in standing 

 vases. On account of their active movement and minute size he called 

 them ''animalcules;" but as they were soon found to make their 

 appearance in great numbers and with remarkable rapidity in watery 

 infusions of organic matter exposed to the air, they afterward received 

 the general name of "infusoria." They present themselves under a 



FIG. 155. 



IJCFCSORIA. of various kinds. 1. Urostyla grandis, from decaying sedge-grass. 2. Paramecium 

 aurelia, from vegetable infusions. 3. Chlamydodon mnemosyne, Baltic Sea water. 4. Kerona 

 polyporum, on the fresh-water polype. 5. Oxytricha caudata, open stagnant waters. 6. Ervilia 

 fluviatilis. clear brook water. 7. Heteromita ovata, on aquatic river plants. Magnified 325 

 diameters. (Ehrenberg and Stein.) 



great variety of forms; so much so that Ehrenberg* described more 

 than 700 different kinds. They are generally provided with cilia 

 attached to the surface of their bodies, and are, for the most part, in 

 constant and rapid motion in the fluid which they inhabit. 



In consequence of the numerous forms of the infusoria, their fre- 

 quent changeability of figure, and their want of resemblance to any 

 previously known organisms, they were thought, by some earlier 

 observers, to have no regular mode of generation, but to arise indis- 



Die Infusionsthierchen als vollkommene Organismen. Leipzig, 1838. 



2M 



