POLLIWOG PROBLEMS 111 



in a saucer, and examine them carefully under 

 a good magnifying glass, or, better still, through 

 a low-power microscope lens. 



You will notice that the tiny spheres are not 

 uniformly coloured but that half is whitish. If 

 the eggs have been recently laid the surface will 

 be smooth and unmarked, but have patience and 

 watch them for as long a time as you can spare. 

 Whenever I can get a batch of such eggs, I never 

 grudge a whole day spent in observing them, for 

 it is seldom that the mysterious processes of life 

 are so readily watched and followed. 



Keep your eye fixed on the little black and white 

 ball of jelly and before long, gradually and yet 

 with never a halt, a tiny furrow makes its way 

 across the surface, dividing the egg into equal 

 halves. When it completely encircles the sphere 

 you may know that you have seen one of the 

 greatest wonders of the world. The egg which 

 consisted of but one cell is now divided into two 

 exactly equal parts, of the deepest significance. 

 Of the latter truth we may judge from the fact 

 that if one of those cells should be injured, only 

 one-half a polliwog would result, either a head 

 or a tail half. 



Before long the unseen hand of life ploughs an- 

 other furrow across the egg, and we have now 

 four cells. These divide into eight, sixteen, and so 

 011 far beyond human powers of numeration, until 

 the beginnings of all the organs of the tadpole 



