THE TALE OF TADPOLES 33 



buoy up the eggs and at the same time obviate overcrowd- 

 ing. In the little chinks between the spheres there are often 

 groups of green unicellular plants which liberate oxygen 

 in the sunlight and use up the carbonic acid gas which the 

 developing eggs produce a most profitable association, a 

 miniature illustration of the balance of Nature. But there is 

 a fauna as well as a flora of frog-spawn, and the chinks are 

 tenanted by small fry such as water-fleas and rotifers 

 some of which eventually loosen the gelatinous envelopes, 

 helping the larval-frogs to escape. Others, it must be 

 admitted, seem to wait to devour. Once again, the en- 

 velopes of jelly are useful in lessening the risks of jostling 

 which might be fatal to the delicate embryos when the 

 wind raises waves in the pond, or when a water-hen or coot 

 splashes in among the spawn. Moreover, the j elly seems to be 

 unpalatable to most water animals, and it is so slippery that 

 few birds can make anything of it. Finally, it may be that 

 the clear spheres serve as so many greenhouses, enabling the 

 ova to make the most of the sun's rays. All this illustrates 

 the scientific view of Nature as an arena where efficiency in 

 any form always counts. 



About a fortnight or three weeks after the individual 

 life began, that is, after fertilisation, the minute larvae are 

 hatched from the delicate envelope of the ovum, and begin 

 to wriggle about in the dissolving jelly. They are somewhat 

 awkward-looking, half-made creatures at first, and when they 

 emerge from the jelly they are mouthless, limbless, eyeless, 

 and gill-less. They attach themselves, often in long rows, 

 to water-weed, the adhesion being effected by a paired 

 cement-gland below the position of the future mouth. A 

 bulging on the ventral surface of the body indicates the posi- 

 tion of the still unused remains of the legacy of yolk. 



Soon after hatching three pairs of external gills grow out, 

 the first much the largest, one upon each of the first three 

 3 



