INFUSORIAL ANIMALCULES ; RHIZOPODA. 555 



common stem ; and sometimes this ramifies and subdivides, so 

 as to exhibit a completely arborescent form, analogous to that 

 of the Polypifera. The circular arrangement of the cilia around 

 the mouth, and the mode in which these organs are employed in 

 obtaining food, has occasioned the Vorticellce and the Wheel- 

 Animalcules to be confounded together. 



1218. The principal families which have been lately eliminated 

 from the Infusoria, and transferred to the Vegetable Kingdom, 

 are the Volvocinece and the Bacillarice. The former are globu- 

 lar organisms, which may be commonly found in ponds, moving 

 slowly through the water by the agency of numerous filaments 

 which project from little green points upon their surface. The 

 Bacillarice, or Diatomacece, are furnished with silicious shields, 

 and are usually found united into filaments of various forms. 

 They are especially interesting from the vast accumulations of 

 their shields which are found fossil in different parts of the 

 world, whole beds of earth, and even of stone, being almost ex- 

 clusively composed of their microscopic remains. 



CLASS II. RHIZOPODA. 



1219. In the animals forming the second class of the Pro- 

 tozoa, the general organisation, as f^f as it can be made out, 

 appears to be very similar to that of the Infusoria ; but we find 

 no trace of a firm external layer, bearing cilia, such as occurs in 

 most of the species of the preceding class. On the contrary, the 

 whole body appears to consist of a homogeneous mass of jelly, 

 capable of extension in various directions ; and the only internal 

 organs that can be detected, are the contractile vesicles and 

 the nucleus. 



1220. The best-known of these Animalcules is the Amoeba 

 diffluens, called the Proteus by microscopic observers, a small 

 gelatinous creature, which is found in our fresh waters. Its 

 movements are effected by throwing out processes from any part 

 of its body ; these appear to act as feet, and the little mass of 



