THE LAWS OF HEREDITY 



CHAPTER I 

 THE CHARACTERS OF LIVING BEINGS 



The cell Conjugation of cells The germ-plasm Hereditary tendencies 

 or potentialities The stimuli under which living beings develop Nutriment, 

 injury, use, etc. The evolution of useful reactions to stimuli Almost all 

 living structures are capable to some extent of repairing injuries, but not nearly 

 all are capable of growing under the stimulus of use The real meaning of 

 the terms inborn, acquired, and inheritable The confusion and waste of labour 

 which has resulted from a use of inaccurate and misleading terms. 



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I. ^ | ^\HE material basis of all known life is the living 'cell.' A 

 cell is a mass, usually very minute, of a jelly-like sub- 

 stance known as protoplasm. The lowest plants and 

 animals are single cells. Higher living beings are compounded of 

 two or more, it may be billions of cells, most of which are adherent 

 together, though some for example, the blood-cells may move 

 freely within the organism. Cells multiply by self-division, the 

 mother-cell distributing itself between the daughter-cells. In the 

 case of unicellular or single - cell organisms the daughter-cells 

 separate, but in higher types they remain together. As a conse- 

 quence a man, for example, is an organised colony or community, 

 a family or tribe or race of cells, all of which have descended from 

 a common cell-ancestor, the fertilized ovum or egg. Speaking in 

 general terms, the descendants of a unicellular organism closely 

 resemble their ancestor. Each individual is able to continue the 

 species by self-division, and each performs all the functions neces- 

 sary to existence, such as the procurement of food. But the 

 descendants of the fertilized ovum, though they remain together, 

 indeed because they remain together, break up into many types. 

 Thus, in a man there are skin-cells, bone-cells, nerve-cells, various 

 kinds of gland-cells, and others. In other words, the members of 

 this community are specialized in form and function. Each has a 

 special shape and structure whereby it is adapted to perform some 

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