Il] AMOEBA 19 



process is called fission . and it is found that the nucleus always 

 Reproduction divides into two before the body as a whole shows 

 and Encyst. any signs of the process. When Amoebae are exposed 

 to unfavourable conditions, such as the drying up of 

 their surroundings, they have the power of enclosing themselves in 

 a cyst. They draw in all their pseudopodia and assume a spherical 

 form, and the cyst appears as a membrane on the outside which 

 then thickens. Once enclosed within its cyst, Amoeba can be blown 

 about like a particle of dust, and in this way we can account for 

 the fact that we sometimes find Amoeba in infusions, that is, solu- 

 tions made by allowing some animal or vegetable matter to stand in 

 water exposed to the air. If we put some hay or meat into perfectly 

 pure water and expose it to the air, it will putrefy; this is due to 

 the development of minute microscopic plants called Bacteria, the 

 spores of which are carried by the air : at a later stage, various 

 Protozoa and sometimes Amoebae will appear. At one time it was 

 supposed that both Bacteria and Protozoa were spontaneously 

 developed out of the dead meat, but it has been shown that if the 

 water and meat be boiled, so as to kill any spores which may be in 

 them, and the mouth of the vessel plugged with cotton-wool whilst 

 steam is issuing, so that the air penetrating from outside through 

 the interstices of the wool has all the spores it may carry strained 

 off before it comes in contact with the water, neither Bacteria nor 

 Protozoa will appear. The cyst which invests the body of the 

 Amoeba is the first instance we have met with of what is called a 

 secretion. A secretion has already been denned as dead substance 

 which is of use to the animal, and which is produced by the 

 decomposition of protoplasm. 



In one or two cases an Amoeba enclosed within its cyst has been 

 seen to break up into a number of rounded germs which were 

 eventually set free by the breaking of the cyst and each of which 

 then took on the form of a minute Amoeba. This process is called 

 sporulation and the germs to which it gives rise spores. It is 

 unknown whether every species of Amoeba sporulates and if so 

 under what conditions this occurs. 



When we were describing the endoplasm of Amoeba above, we 

 called it granular, owing to its containing solid particles. It must 

 however be remembered that the endoplasm is a colloid solution 

 or sol. whilst the ectoplasm is a "gel." In the sol. are dissolved 

 the oxygen necessary for life and the carbon dioxide which has 



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