2 THE PROTOZOA-THE DAWN OF LIFE 



now very generally considered that the dawn of life took place 

 upon the wet sands, or in the quiet waters of some shallow sea 

 of the primeval world ; for the warm water-logged mud of the 

 seashore would have been a specially suitable medium, owing to 

 its constant temperature, its moisture, and soft surface, for the 

 development and support of the first forms of animal life, and for 

 the accumulation of the first formed organic matter from which 

 these primordial organisms probably sprang ; for the essential 

 chemical constituents of living matter are all soluble in, and con- 

 stituents of, sea-water. 



The Protozoa are all organisms characterised by the compara- 

 tive simplicity of their structure, and by existing either as single 

 cells or colonies of similar cells, mere repetitions of each other, 

 each capable of maintaining an independent existence. It is to 

 these primitive organisms that we must first turn our attention 

 if we are fully to realise the significance of all the beautiful and 

 wonderful creatures, with their varied shapes and habits, to be 

 met with in the animal kingdom, and how, step by step, the 

 higher forms of animal life have been gradually evolved from 

 simple forms. 



Of the great antiquity of the Protozoa we have a graphic 

 record in the rocks of the earth, for their fossil remains have been 

 found in the oldest known rocks that have retained any indication 

 of the existence of life on the earth. The limestones and sand- 

 stones of many mountain ranges are largely composed of the fossil 

 remains of Protozoa ; the wonderful pyramids of Egypt are really 

 vast piles of an extinct Protozoon whose skeleton was about the 

 size of a large pea ; while the white chalk cliffs of old England 

 are largely composed of the skeletons of these organisms ; for 

 while some Protozoa remain soft, jelly-like specks of changing 

 form, leaving no record of their existence, others evolve the most 

 exquisite skeletons of lime and silica, imperishable, outlasting the 

 mountains they served to form. 



We will begin our study of these primitive forms of animal 

 life by examining a tiny microscopic creature to be found in the 

 mud at the bottom of ponds and streams, and in the shallow pools 

 on the seashore. It is called the Amoeba, from an old Greek word 

 which means changeful, and when first discovered was called the 

 " Proteus Animalcule," after the changeable sea god of the ancient 



