l6o ANIMAL LIFE OF THE BRITISH ISLES. 



When the pairing season arrives quite early, usually about 

 the middle of March, but sometimes in February all the Frogs 

 that have just come out of hibernation select their mates. Any 

 pool of water will do, however transient, and they often make 

 mistakes in this matter, their egg-masses being left high and 

 dry when the waters dry up. The eggs are deposited in a mass 

 of a thousand to two thousand at the bottom of the water, and 

 at first they are only about a tenth of an inch in diameter, but 

 the gelatinous covering absorbs so much water that they swell 

 up to a third of an inch. There is a corresponding lightening 

 of the mass, which floats to the surface and is available for 

 observation. Each of the little jelly-spheres is seen to have a 

 black centre the egg proper with a white spot on the lower 

 side. If the spring is an average one, in about four weeks' 

 time the black specks will have developed into brown larvae or 

 tadpoles, and having escaped from the egg these will be 

 clinging to the remains of the jelly mass by means of a pair of 

 suckers on the underside of the head. There are at present no 

 indications of limbs head, body and tail, like those of a fish, 

 merge one into another. Even the gills are not yet developed, 

 though what we may term the buds of them are seen on the 

 bars separating the slits behind the head on each side. 

 These buds soon expand into gill-plumes through which the 

 blood circulates, taking up oxygen from the water that passes 

 between them. There is as yet no mouth, but this will soon 

 open, and horny plates on its jaws will enable the tadpole to 

 crop soft vegetable matter, upon which it subsists chiefly. Later 

 on, the gill-plumes will be hidden by a flap which grows over 

 them. The full series of stages in this development may easily 

 be watched by keeping a few tadpoles in a glass of water with 

 a little growing pond weed. 



Ultimately, the limbs appear. Though all four develop 

 simultaneously, the hind pair appear first, because the fore 

 limbs are at first hidden by the flap which grew over the gills. 



