CHAPTER III 



THE BEHAVIOR OF INFUSORIA; PARAMECIUM 



Structure; Movements; Method of Reaction to Stimuli 



introductory 



The name Infusoria is applied to those unicellular organisms (aside 

 from bacteria) that swim by means of cilia or flagella, as well as to a few 

 others. The organs of locomotion are protoplasmic processes on the 

 body surface. Where these are short and numerous, they are called 

 cilia; where they are long and the organism bears but one or a small 

 number, they are called flagella. The organisms bearing cilia are 

 classed together as Ciliata ; those with flagella are the Flagellata. Fig- 

 ure 31 shows a number of characteristic forms of the Ciliata. Along with 

 the infusoria we shall take up other unicellular organisms or develop- 

 mental stages that swim by means of such protoplasmic processes, — 

 for example, spermatozoa and swarm spores. 



The infusoria are commonly found, as the name implies, in infusions 

 of decaying animal and vegetable matter. One of the commonest and best 

 known of the infusoria is Paramecium, found in water containing de- 

 caying marsh plants, or in hay infusion with which some marsh or pond 

 water has been mixed. The behavior of Paramecium has been studied 

 more than that of any other infusorian, so that we shall take this up 

 first as a representative of the group. The behavior of other species 

 will be then examined to discover how far the relations in Paramecium 

 are typical, and to bring out differences — especially points for which 

 Paramecium is not a favorable object of study. 



I. Behavior of Paramecium; Structure 



Paramecium (Fig. 32) is a whitish, cigar-shaped animal, Uving in 

 immense numbers in decaying vegetable infusions, and visible to the 

 naked eye as a minute, elongated particle. The anterior part of the 



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