n6 Polywog Problems [THIRD WEEK 



into many cells, the lichen, violet, tree, worm, crab, but- 

 terfly, fish, frog, or other higher creature is formed. A 

 little embryology will give a new impetus to our studies, 

 whether we watch the unfolding leaves of a sunflower, a 

 caterpillar emerging from its egg, or a chick breaking 

 through its shell. 



The very simplest and best way to begin this study is 

 to go to the nearest pond, where the frogs have been 

 croaking in the evenings. A search among the dead leaves 

 and water-soaked sticks will reveal a long string of black 

 beads. These are the eggs of the toad; if, however, the 

 beads are not in strings, but in irregular masses, then they 

 are frogs' eggs. In any case take home a tumblerful, place 

 a few, together with the thick, transparent gelatine, in 

 which they are encased, 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 



