4 Elementary Zoology. 



The body of the amoeba, therefore, is constantly wasting 

 away and being as constantly renewed by the taking in of food, 

 which must be in the form of living or dead animal or vegetable 

 matter. 



But the animal performs other functions. 



When the creature has attained to a certain size, which 

 differs in different species, and even in individuals, it divides 

 into two ; the nucleus divides and then the protoplasm, so that 

 where there was one amoeba there are two. This process 

 under favourable circumstances is continually repeated. But it 

 has its limits. After a certain number of generations have been 

 thus produced by simple fission — the number varying with the 

 species, and not being accurately fixed — this method of repro- 

 duction ceases. Another kind of generation comes into play. 

 Two amoebae approach and fuse together, the nuclei joining 

 and the protoplasm being commingled. After a longer or 

 shorter period of conjugation the two may become surrounded 

 in a delicate cyst, and break up into a number of minute spores, 

 which gradually attain to the size of the parents after the 

 rupture of the case ; or the two may separate, and, refreshed 

 by the union of the nuclei and protoplasm, go on dividing by 

 the process of fission. This conjugation must not be confused 

 with the ingestion of one amceba by another, though in some 

 cases it is doubtless difficult to distinguish between the two — 

 between hunger and love. 



The question may be asked. Why should an amoeba 

 divide? why should it not go on growing indefinitely? The 

 question is easier to ask than to answer. In considering the 

 matter it must be borne in mind that possibly the viscid and 

 semifluid protoplasm cannot hold together in droplets above 

 a certain size, and (more important) that the surface does not 

 increase in extent pari passu with the contained mass ; hence 

 the power of ingesting food and excreting waste products may 

 be not sufficiently rapid to keep pace with the growing mass. 

 Accordingly the animal divides into more conveniently sized 

 pieces. 



The amceba then moves, responds to stimuli, feeds, 

 excretes, grows, and reproduces itself. These are among the 



