TYPES OF PROTOZOA. 105 



Special Types. 



Amoiba—a. type of Rhizopods, especially of those in which 

 the outflowing processes of living matter are blunt and finger- 

 like (Lobosa). 



Description. — Arnxba proteus and some other species are 

 found on the muddy bottom of ponds ; A. terricola occurs 

 in damp earth. Some are just large enough to be seen with 

 the unaided eye. They glide along the surface of stone or 

 plant by protruding and retracting blunt processes, and 

 their changefulness merits the old (1755) popular name of 

 " Proteus animalcule." The food, which consists of minute 

 Algse such as diatoms, or of vegetable debris, is sur- 

 rounded by the finger-like processes, and engulfed along with 

 drops of water, which form food vacuoles in the cell-sub- 

 stance. Round the margin, which sometimes shows an 

 apparent radial striation, the cell-substance is firmer and 

 clearer than in the interior, where granules and debris often 

 obscure the normal clearness. A single nucleus lies in 

 the centre of the cell. Indigestible debris and waste par- 

 ticles are got rid of, by being left behind in the onward 

 flowing of the animal, and two contractile vacuoles seem to 

 aid in the excretion of the finer waste-products. 



Life-History. — In favourable, nutritive conditions, the 

 Amceba grows. At the limit of growth it reproduces by 

 dividing into two. In disadvantageous conditions, such as 

 drought, it may become encysted and lie dormant for a 

 while. The return of prosperity revives it, and it bursts 

 with renewed energy from the cyst. The permanent conju- 

 gation of two AmcebcB has been observed, and it is said that 

 a mode of spore-formation occasionally occurs. 



Paramxcium — a type of Infusorians, especially of those 

 which are uniformly ciliated. 



Description. — Specimens of Paramcecium may be readily 

 and abundantly obtained, by leaving fragments of hay to 

 soak for a few days in a glass of watisr. A few Infusorians 

 have been lying dormant about the plant, they revive and 

 multiply with extraordinary rapidity. They are abundant 

 in most stagnant pools, and are just visible when a test tube 



