An Introduction to a Biology 



moment no further blood-supply to it would be 

 possible. Up till the moment when the wheel was 

 full-grown, wheel and axle would be of one piece. 

 Once the last drop of blood required for the full 

 development of the wheel had passed into it, the 

 blood-vessels and other tissues in the wheel would 

 begin to atrophy, and a cylindrical separation would 

 take place between axle and wheel, or between axle 

 and socket, and the wheel would be free ; and not 

 till then would the wheel be in esse a wheel ; for 

 then, and not till then, would the wheel possess the 

 essence of the wheel, which is rotability. Up till that 

 critical moment in the life-history of the cyclo- 

 phorous vertebrate it would be a helpless tetra- 

 cycle with the brake jammed on. An attempt to 

 move the animal long before the liberation of the 

 wheel would spoil the wheel for future use by wearing 

 it flat in one place ; a similar attempt nearer the 

 time of the liberation of the wheel would produce 

 death or grave disorder by haemorrhage of the axle. 

 And then, when the wheel had become rotable in 

 the fullness of time, the animal could not move 

 of his own accord unless only his hind limbs had 

 been modified into wheels and his front ones were 

 legs ; if he were a tetracycle on the level he would 

 remain stationary unless he had domestic animals 

 to pull him about ; if he were on the side of a hill 

 he would probably be wrecked. This attempt to 

 visualise the origin of the wheel -before evolution 

 had got on to the extra -corporeal stage seems to 

 me to show that the wheel would not have been of 

 any use before the mind had gone far enough to 

 conceive of a cart, and to make the tools good enough 



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