iv MECHANISM AND TELEOLOGY 307 



experiment has shown that the mutilation of an embryo at 

 an early stage may induce a far-reaching readjustment. In 

 some cases, for example, the daughter-cell produced by the 

 first division of the fertilised ovum, which normally 

 develops into one half of the embryo may, upon the 

 artificial removal of its fellow, be made to do duty for the 

 whole. It may develop not as usual into the half but into 

 the entire organism. Similarly, and on more familiar lines, 

 any deviation of one tissue from the normal will involve 

 a response on the part of other tissues. A curvature 

 of the backbone alters the whole upper part of the figure, 

 and a number of tissues must accommodate their shape 

 accordingly. The cells of the skin, for example, multiply 

 only so far as is necessary to cover the dwarfed skeleton. 

 Similarly, in the adult organism, lesions and abnormalities 

 of all kinds are met with special growths of suitable tissue. 

 Constant use of the hands does not wear away their sub- 

 stance with friction as the surface of an inanimate object 

 would be worn away. It stimulates the production of 

 horny substance by the cells of the epidermis, and the 

 result is a hand not less but better fitted for its work. The 

 athlete's heart braces itself to its excessive labour by 

 thickening its muscle. Even the bony tissues adapt them- 

 selves to special strains and alter their structure to meet 

 new conditions. c If the bone is broken and heals out of 

 the straight, the plates of the spongy tissue become re- 

 arranged, so as to lie in the new direction of greatest 

 tension and pressure ; thus they can adapt themselves to 

 changed circumstances. 5 1 The elementary truth of prac- 

 tical life, that the living being grows and flourishes through 

 and by means of its difficulties, dangers and toils, rests on 

 this general reactive elasticity of the organism, that is, on 

 the capacity of each part to adapt itself with structure and 

 function to the needs of the whole. 



6. Thus, alike in the growth, modification, and activity 



of vital structure, we see that close interdependence of parts, 



or what is the same thing, that adjustment of part to whole 



which our definition of organic unity required. The 



1 Weismann, Romanes Lecture, p. 1 5 . 



