a7i THE WOELD OF LIFE 



characters. A similar illustration, at a later period of life, is 

 that of an infant Avhich from birth is fed on cow's milk, yet, 

 if it lives, possesses only human characteristics. 



This nucleus^, therefore, which, when fertilised, has such 

 marvellous powers and properties, is tlie seat of heredity and 

 development. What is it that gives it this power ? What 

 is the agency that sets in motion a whole series of mechanical, 

 chemical, and vital forces, and guides them at every step to 

 their destined end ? Again, I urge, let us consider what we 

 have to explain. The matter of the fertilised egg is the mil- 

 lionfold complex substance called protoplasm. It is also 

 mainly living protoplasm. AVhat power gave it life ? It is 

 also (in its essential part, the nucleus) already highly differ- 

 entiated — it is organised 'protoplasm. What poiver organ- 

 ised it ? It is a liquid or semi-liquid substance with slight 

 cohesion ; it gradually forms a cell, which divides and sub- 

 divides, till at a certain point the globular mass or layer of cells 

 bends inward upon itself, forming a hollow sac with outer and 

 inner walls. What power determines the cell-mass to take 

 this or other well-defined shapes ? Then, as cell-division and 

 specialisation go on, the rudiments of muscle and bone are 

 formed with totally distinct properties — the one with im- 

 mense contractility and tensile strength, the other with great 

 hardness and rigidity. Who or what guides or determines 

 the atoms of the protoplasmic molecules into these new comibi- 

 nations chemically, and new structures mechanically ? — com- 

 binations and structures which all the chemists and physicists 

 of the world are powerless to produce even when they have the 

 ready-formed protoplasm given them to start with ? Then as 

 the process goes on in an ever-increasing complexity which 

 baffles the microscope of the observer to follow, never diverg- 

 ing at any one point from the precise mode of change which 

 alone leads on to the completed living organism, we are asked 

 to be satisfied with millions of ^^ gemmules," " fundamental 

 units," " determinants," etc., which actually do build up the 



