CHAPTER IX 



THE DIVIDED LABOURS OF THE BODY 



I. Division of Labour — 2. The Functions of the Body : Movement; 

 Nutrition ; Digestion ; Absorption ; The Work of the Liver 

 and the Kidneys; Respiration; Circulation; The Changes 

 ■within the Cells ; The Activities of the Nervous System — 

 3. Sketch of Psychology 



I. Division of Labour. — The simplest animals are one- 

 celled ; the higher animals are built up of numberless cells. 

 All the processes of life go on within a single cell. In a 

 many-celled animal the labours of life are divided among 

 the various groups of cells which form tissues and organs. 

 The history of physiological development is the history of 

 this division of labour. 



When a dividing cell, instead of separating into two 

 distinct masses, remained, after the division of its nucleus, 

 with the two daughter masses lying side by side, joined 

 together by strands of protoplasm, then the evolution of 

 organic form took a distinct step upwards, and at the same 

 time arose the possibility of greater activity, by means of 

 the division of labour. For when the process had resulted 

 in the formation of an organism of a few dozen cells, 

 arranged very likely in the form of a cup, the outer cells 

 might devote the greater part of their energies to movement 

 and the inner cells to the digestion of food. In the com- 

 mon Hydra the body consists of two layers of cells arranged 

 to form a tube, the mouth of which is encircled by tentacles. 



