REPRODUCTIVE PROCESS IN ANIMALS 53 



with. A slight movement of the head or arm, a 

 slight puff of wind, a slight touch by a passer-by would 

 be enough to overturn the body w r ere it not instantly 

 met by a slight automatic increase in the tension of 

 certain of the muscles. As a matter of fact, the body 

 when apparently standing still is never really standing 

 still for a moment : it is constantly commencing to fall 

 over to one side or the other, and is constantly being 

 automatically checked and pulled back towards the 

 vertical. Hundreds of bundles of muscle-fibres are at 

 work the whole time, all co-operating together, each 

 doing exactly its share no shirking, no strikes, no lock- 

 outs, every unit loyally doing its bit. If our friend at 

 the corner were to realise that wonderfully co-ordinated 

 activity within his own body it would surely break his 

 heart : he would fling himself into the river ; he might 

 even take to work ! 



What I have been saying so far is merely to impress 

 upon you what unsuspected complexities underly even 

 the simplest actions of living creatures. The reproductive 

 process is not one of these simplest processes but probably 

 the most tremendously complex of them all. How it 

 is that a speck of matter so small as to be invisible except 

 under a powerful microscope, such that no details of its 

 intimate structure can be made out even with the very 

 highest magnification, can reproduce all the details of 

 structure and function of the human being, nay of an 

 individual human being with his obscure peculiarities 

 of appearance, of manner, or of habit, is a mystery which 

 must surely for all time transcend scientific knowledge. 

 And yet, though the ultimate nature of this as of other 

 vital processes is unknown, a vast and ever increasing 

 amount of knowledge has been accumulated regarding 



