THE BREEDING BEHAVIOUR OF THE FROG I59 



channel. Frogs arc plentiful, far more so than in the surrounding 

 country, and spawn in many of the pools, and also on a weed mat in 

 the main stream of the drainage channel. The stream is rich in 

 vegetation, and the w^eed of the mat was encrusted with sessile algae. 

 It was no isolated aberration, for there were probably a hundred 

 clumps on the mat, as far as I could judge from the bank, for the water 

 was too deep for me to reach the spawn by wading. The conditions 

 in this quarry, where frogs flourish, bears a remarkable resemblance 

 to the glacial moraines among which perhaps tliis species was evolved. 

 Not only is the sand and gravel of Quaternary glacial origin, but the 

 machines pile it up into ridges of shifting material, and there is running 

 water everywhere, much as in natural moraines of the present day. I 

 have seen tadpoles of this species in a pool in just such loose material 

 beside the Rhone, below the snout of the glacier. 



Pollution 



Many ponds are polluted by cattle and in other ways. I think that 

 this is a favourable factor. In the stream out of Jack's Pond, there were 

 several sources of pollution. The main one was derived from a large 

 heap of slaughterhouse refuse, the accumulation of years, and con- 

 tinually replenished. There were smaller sources from the drainings 

 from a cowshed and from a very poor sewage puiification plant. In 

 one year, one clump of spawn was laid almost exactly in the middle of 

 the patch of green, composed o£Euglenay that marked the entry of the 

 pollution from the refuse heap into the main stream. The mud at the 

 main spawn site was composed of diatoms in great variety and un- 

 usually large size. Besides this case, I have known of two other spawn 

 sites in. which sewage was present, and have had another reported to me. 



The Breeding Behaviour 



The earhest description of the breeding behaviour of this animal is 

 apparently that of Swammerdam (163 7-1680, English translation of 

 1758). No important original observations were made until Rosel 

 von Rosenhof (1758), an Austrian Count, pubhshed his book on the 

 European Anura occurring near his home. Rdsel's book was sump- 

 tuously produced, with many beautiful coloured plates from his own 

 paintings. It would be quite wrong to suppose that these accounts are 

 merely part of scientific history. At the cost of much labour, I had 

 already made my observations before I saw these books, and I read 



