CHAPTER V. THE AMCEBA AND THE CELL. 



1. The Amoeba. We have now seen, in a very general 

 way, how the activities that constitute the life of the rabbit 

 are rendered possible, and can go on to a more detailed 

 study of the structure of the rabbit's body, and particularly 

 of the microscopic structure, or histology of its tissues. 

 Before doing so it will be an advantage to turn aside to 

 another of our animal types the simplest in structure on 

 our list, as the rabbit is the most complex. 



Amoeba is the name given to a small creature that occurs 

 in abundance in the mud at the bottom of fresh-water 

 ponds. Like the rabbit, it is a vegetable- eater, but its 

 mode of life is infinitely simple compared with that of the 

 complex organism we have been studying. Examined under 

 the microscope, the first thing that strikes one about Amoeba 

 is its irregularity of shape, and careful observation for a 

 few minutes shows that the shape is continually changing 

 a characteristic which led the first workers at the 

 microscope to name it " the Proteus animalcule." This 

 is due to the fact that the substance of which it is composed 

 called protoplasm is semi-fluid in nature. Careful 

 examination shows that the protoplasm is not the same all 

 through ; there is an outer, clear, transparent layer called 

 the ectoplasm and a central mass full of minute granules, 

 the endoplasm. The constant change in shape is effected by 

 the flowing of protoplasm towards certain points where, in 

 consequence, projections appear, called pseudopodia. Of 

 course the protoplasm that enters into them is withdrawn 

 from somewhere else, and therefore if the formation of 

 pseudopodia is mainly in one direction, the amrcba must be 

 changing its position as well as its shape : in this way 

 locomotion is effected. 



2 Nutrition of Amoeba. In the same mud in which 

 we find amoabse, there are abundant microscopic plants 



