CHAPTER IX 



PROTOZOA 



The animal built up of cells. Principle of division of labour. The 

 greater the division of labour, the higher the animal's organisation. 

 Multicellular and unicellular animals. The protozoa, their form 

 and reproduction. Structure of an animal in its development 

 from the ovum onwards from rudimentary parts. Origin of the 

 germ-cells. Outlines of a theory of heredity. Amphimixis of 

 the protozoa. Origin of sexual reproduction. Formation of seed 

 and ova. Continuity of the germ-cells. Are any animals 

 immortal? Death is not common to all animals. Origin of 

 death. Permanent and temporary life. Has life come from the 

 stars ? Origin of life on the earth, spontaneous generation. How- 

 it is to be conceived. The first development of living matter. 

 Formation and significance of the cell-nucleus. Significance of 

 the fundamental parts. Relation of the rudimentary parts in 

 amphimixis. When life is extinguished. 



To a certain extent we may compare organisms to 

 edifices in our towns. Just as our buildings differ 

 enormously in size and structure, yet are generally 

 composed of the same elements, the bricks, so we find 

 the same elementary units in all vegetal and animal 

 bodies. In the course of its embryonic development 

 every organism is built up like a house. Its life 

 begins with one structural element. To this numbers 

 of fresh ones are added until at last the highest point 

 is reached ; the living thing has attained its full size, 

 and it would be idle to attempt to count its constituent 



units. 



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