26 MECHANICAL FUNCTIONS. 



achs ; so that the food which has been taken in by one 

 of the mouths, contributes to the general nourishment of 

 Fig. 14. the whole mass of 



aggregated polypi. 

 These curious facts 

 were discovered by 

 Cuvier, and are re- 

 presented by fig. 14, 

 where the stomachs 

 of the three polypi, 

 with their tentacula spread out, are seen communicating 

 at their lower extremities with a canal, which thus be- 

 comes a common stomach to the whole colony. 



INFUSORIA. 



The Infusory insects, or Infusoria, were so named 

 from the circumstance that they always appear during 

 the warm seasons, in water in which vegetable or animal 

 substances have been infused. Hence they exist in 

 stagnant ditches and pools of water, every where du- 

 ring the summer and autumn. These animals are 

 generally too minute to be distinguished by the naked 

 eye, and therefore it is to microscopic observations that 

 we owe our knowledge of their existence and habits. 



Former writers on natural history have called these 

 animalcula, monads, and have regarded them as occu- 

 pying the very lowest rank of animal creation. Some 

 have even expressed doubts whether they really belong 

 to the animal kingdom ; but would rather consider them 

 as molecules, or the elementary particles of organic be- 

 ings, separated from each other by chemical decompo- 

 sition, but retaining the power of voluntary motion. 



The Infusoria, during the last century, have been the 

 object of veiy laborious microscopical research ; no nat- 

 uralist considering himself accomplished until he had 

 spent a considerable portion of time in observing the 

 motions and studying the characters of these animated 

 particles. Many theories, conjectures, and disputes 



Whence do the infusoria derive their name 7 What was the former 

 .name for infusoria 7 



