THE FACTORS OF EVOLUTION 147 



features may be illustrated by a few instances. The tail-feathers 

 of a Japanese "phoenix" attain a length of 4 metres; good 

 laying breeds like Wyandottes and Hamburgs may reach an 

 annual production of 200 eggs. Toulouse fattening-geese fre- 

 quently reach a weight of 15 kilogrammes; and finally the 

 merino sheep, in particular the so-called electorals, produce wool 

 at the rate of 6,000 hairs per square centimetre, whilst ordinary 

 breeds have only about 1,000. 



In most cases the breeder will be unable to modify, by means 

 of artificial selection, any one organ without affecting, even 

 though it be undesirable, other parts of the body. If, for 

 instance, it were desired to breed goats with such enormous horns 

 as are carried by the Alpine Steinbock (Capra ibex] the process 

 would inevitably lead to a modification of the entire organization 

 of the affected animals. The skull would become thicker and 

 stronger to be able to carry the heavy burden of the horns ; 

 similarly the muscles of the neck and back would increase in 

 strength, and the neck tendon would become thicker ; the spinous 

 processes of the cervical and dorsal vertebrae would, therefore, 

 become longer and stronger in order to meet the greater demands 

 made upon the muscles of the neck. Further, the skeleton parts 

 as well as the muscles of the anterior legs would adapt themselves 

 to the greater burden, and this, again, would react upon the 

 nervous and vascular systems. We see, therefore, that even the 

 transformation of a comparatively unimportant part of the body* 

 the horn, necessitates a corresponding transformation of the rest 

 of the body. 



Every organism is, as it were, in a state of fluctuating 

 equilibrium. Its single parts are mutually dependent, so that 

 each modification of one organ disturbs the harmony of the 

 whole, and produces compensating modifications in other parts. 

 This remarkable interdependence of different systems and parts 

 is called the correlation of the organs, an important factor in the 

 formation of new species and breeds. 



A remarkable case, in which the correlation of the various 

 parts may be clearly perceived, was recently observed in a deer 

 park. Shortly after a large red deer had thrown his antlers 

 he fractured his left anterior leg. It was set with every possible 

 precaution, and the healing progressed favourably. But whilst 



