INTESTINAL PROTOZOA, AMCEBA 229 



ectosarc can be readily seen when pseudopodia are 

 thrown out, but it is difficult to see in the resting animal. 

 The pseudopodia are very broad and only one or two 

 are protruded at a time. The nucleus in unstained 

 specimens can be readily seen near the centre of the cell. 

 Movement is active at or near blood-heat, but is retarded 

 or stopped at lower temperatures. Multiplication of the 

 amoeba may take place by simple division ; the nucleus 

 divides, and the protoplasm then divides, so that two equal 

 individuals are produced. This is the asexual method of 

 reproduction, and takes place readily where the conditions 

 for existence are favourable. The second method may be 

 considered as a rudimentary sexual process, though the 

 conjugation is by fusion of two chromatin masses derived 

 from one nucleus and not of two separate cells. 



If considered as asexual process it would be an instance 

 of autogamy. In this method the amoeba becomes 

 encysted. The nucleus divides into two, and each of 

 these nuclei after extruding polar bodies again divides 

 into two. The four nuclei thus produced conjugate in 

 pairs, so that the number of nuclei is again reduced to 

 two. These two nuclei each divide into two and then 

 again divide so that there are eight nuclei, and these with 

 the protoplasm segmented round them form eight young 

 amoebae which are still contained in the cyst (fig. 65). 

 These quasi-sexual encysted forms are resistant, and it is 

 probably this form only that is capable in the parasitic 

 amoebae of retaining vitality in a free form under ordinary 

 meteorological conditions. 



These encysted forms are therefore the important ones, 

 as the infective agents in amoebic infection. In some 

 of the parasitic amoebae in the lower animals the active 

 amoebae are only found in the small intestine. The 

 changes described take place in the large intestine. The 

 amoebae passed in the faeces are all encysted. In such 

 animals, if the intestinal contents were passed rapidly 

 through the alimentary canal, as after purgatives or in 

 diarrhoea, active amoebae would be passed with the stool. 



