INTRODUCTION 1 5 



many other organs to regulate the speed at which 

 the lungs work and the blood flows. Without this 

 rather complicated machinery, the organization of 

 the oxygen supply would be inconc-eivable. The de- 

 velopment of a set of specialized structures is the first 

 step in the business of building up a living organism. 



To say that an animal is an organism means in 

 fact two things : firstly, that it is a system made up 

 of separate parts, and secondly, that in order to 

 describe fully how any one part works one has to 

 refer either to the whole system or to the other parts. 

 Thus it is impossible to describe fully a thighbone 

 without referring to the fact that it is part of a leg, 

 and that one end fits on to a pelvis and the other on 

 to a shinbone. The relation with the other parts of the 

 organism is indeed so close that if an anatomist finds 

 a new fossil bone he can often reconstruct, in general 

 outline, the whole unknown animal to which it belongs. 



There are two possible ways of investigating the 

 organization of an animal. Firstly, we can study in 

 the adult how the organism works as a going 

 concern: we can find out what functions are per- 

 formed by each separate organ; we can discover 

 how the communications between the organs are 

 maintained by the blood and nerves; and we can 

 study the results of removing one or more organs. 

 But all the processes which can be investigated in 

 this way will be proceeding within the framework 

 provided by the fundamental spatial pattern in 

 which the parts of the animal are arranged, since in 

 the adult this pattern is more or less fixed. We can 



