30 ECOLOGY AND LIFE HISTORY OF THE COMMON FROG 



gone and did not reappear and the water was clear. There were, 

 however, no prominent patches of algae, except at "Sallow." The 

 quantity of spawn, laid on the shallow edge of the pond in about the 

 same place as in 1948, was about the same. It was hatching on loth 

 April. On 23 rd April, the aggregation on the envelopes was still 

 present, but had spread over a larger area. No tadpoles could be 

 collected at "West or "Sallow" on either this date or on 30th April. 

 On 7th May, there was a dense colony at "Spawn Site." The tadpoles 

 were feeding actively on the bottom, occasionally visiting the surface 

 for air but diving at once. A small colony was found at "Sallow" and 

 another at "West," but few were seen elsewhere. Fig. 7 shows that 

 the "Sallow" colony was for the third year in succession the heaviest 

 at about this date. By 13 th May, the difference in the average weight 

 of the tadpoles in the various colonies was even greater, and once 

 again "West," although so near to "Sallow," contained much smaller 

 tadpoles. On 21st May, tadpoles were fairly numerous at "Spawn 

 Site," but the figure shows how small they were — in fact hghter than 

 in the week before. The wet spell then began, and by the 28th the 

 water level had risen. The average weight of the tadpoles at "Spawn 

 Site" was now much greater than on 21st May, and was little below 

 that at "Sallow." On 4th June, the pond was full of water. "West" 

 now provided tadpoles a little larger than "Sallow," and those in the 

 colony at "Spawn Site" were not much smaller. Hot, dry weather 

 now began again. The tadpoles at "Spawn Site" remained at about 

 the same weight, those at "West" actually diminished, but those at 

 "Sallow" continued to grow. By 19th June, the water level was low 

 again. On 25 th June, metamorphosis had begun, and from this date 

 onwards collections could not be made at the usual places because there 

 was not enough water there. On 9th and 1 6th July, the borders of the 

 pond were exposed and evil-smelling, and the water itself was foul. 

 Most of the tadpoles had, however, metamorphosed by this time. 



The tadpole population was larger than in 1948, but very much 

 smaller than in 1947. There were some indications of colony forma- 

 tion in the early part of the season, but the struggling masses of 1947 

 were never observed. 



Metamorphosis in Dagger Lane Pond was always complete by the 

 end of July, and on the whole the tadpoles grew well. The disasters 

 that occurred in some of the other ponds were never seen to the same 

 extent at Dagger Lane. 



