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IX. 



THE EVIDENCE FROM DEVELOPMENT. 



I. THE EARLIER STAGES IN THE LIFE-HISTORY OF ANIMALS. 



AMONG the many features which mark the varied universe of 

 life, none are more universally recognised, or more typical of 

 the living world, than those which herald the production of a new 

 being, and which usher a new form upon the stage of existence. 

 From the shapeless mass of protoplasm that crawls over the water- 

 weed as a microscopic speck, upwards to man himself, the varied 

 processes of development are laid down in orderly sequence and 

 along lines of special kind. Every living being, animal or plant 

 animalcule and whale, the humble lichen and the giant sequoia alike 

 passes through a definite series of changes before attaining the 

 form and likeness of the parent which gave it birth. In virtue of 

 such changes it assumes that parental form. These changes, occur- 

 ring in orderly array, mark its pathway from shapelessness and 

 physiological nonentity to the. characteristic form of its race. It is 

 development which moulds 



The baby figure of the giant mass, 



and from the minute beginnings of life evolves the highest of earth's 

 denizens, or directs the production of the teeming swarms of 

 animalcules that people the stagnant drop, and pass an existence 

 none the less interesting or important because often all unknown to 

 the larger and higher world without. It is this same process of 

 development which, as one phase of living action, draws the sharpest 

 and clearest of boundary lines between the world of life and that of 

 non-living matter. Growth and increase are truly represented in 

 the inorganic world ; but these processes are different in kind from 

 the actions which stamp the development of the animal or plant. 

 The birth of a crystal, although regulated by definite laws, is, after 

 all, a matter of outside regulation alone, and one in which the crystal 

 itself is but a passive agent. New particles are added to the outside 

 surfaces of the old and already formed particles ; and crystal and 

 stalactite thus grow mechanically and by accretion, but without active 

 participation in the work destined to mould and form their substance. 

 Very different are the forces and laws which regulate the pro- 

 duction of the living form. Here the changes of form and the 



