NATURE STUDY IN SCHOOLS. 133 



them. These particles of food are taken in at any point on the suiface of 

 the body and digestion takes place within the body, the nutrutive matter bein<> 

 being retained in bills k.iown as foil vacuoles or food balls (see Fig. 68, E) 

 and within these digestion takes place, the nutritious matter being assimila- 

 ted by the protoplasm in some way. When the process of digestion is com- 

 pleted, the food balls apirjach the outer surface of the body, and break through 

 the ectoplasm at any point, but usually near the posterior end. 



Reproduction. After attaining a certain size, for amoeba like all other 

 known animals, reaches a maximum size, the individual does not die, but 

 divides. That is, there is first a fissure of the nucleus which, in a little time, 

 extends through the entire animal, and we have two amoebae where there 

 was one before. This is the only possible method by which the amoebae are 

 known to reproduce. It is noteworthy that after division no two sections 

 or cells so formed remain joined together, each becomes separate and is, in 

 fact, an individual. 



Irritibility or Nervous System. While we can as yet point to no 

 definite organisms, in which the nervous system of the amoeba resides, the fact 

 that it contracts and expands, that it moves in one direction more than in 

 another, that it takes particular kinds of food and rejects others, and above 

 all, that it reaches out for food, or, in other words, seeks it, without wait- 

 ing for the food to be brought to it, all show that the amoeba possesses a 

 nervous system. Rudimentary and comparatively incomplete as this system 

 is, it is sufficient to meet the wants of the amoeba, guiding it in its search 

 for food and in its selection of it, its movements, etc. 



Encystment. Under certain circumstances, like a change of temper- 

 ature in the water, or upon the gradual drying up of the water in which it 

 Lives, the amoebae contract themselves into the form of a ball, the ectoplasm 

 becomes thickened, and the amoebae remain quiescent for a time. In this 

 condition they are able to withstand considerable drying, and may possibly 

 be blown about by the wind. Upon reaching water again, however, the 

 amoeba becomes animated and resumes its ordinary functions of life. 



Summary. Amoeba is clearly an animal, and as clearly an individual. 

 Although it has the power of assimulating food, it has no fixed mouth, di- 

 gestive system, nor anal opening. There is no apparent respiratory system, 

 but it is probable that the oxygen is taken in through the surface of the body 

 wall, and that the carbon dioxide is ejected in the same manner. The cir- 

 culating system is exceedingly rudimentary, but evidently present. The 

 nervous system, although undiscovered, must be present, for it is evident 

 that the exciting cause of movement, reproduction, etc. comes from within 

 the animal, where the stimulus acts upon the protoplasm, which responds. 

 Reproduction is of the simplest kind, by division, and as far as definitley 



