THE EGGS AND YOUNG TADPOLES I5 



regarded as almost a diagnostic character of the eggs of these species. 

 This should be kept in mind when reading Chapter 8. 



The adhesive properties of the newly laid eggs is often of no apparent 

 use to the animal. R. temporaria is usually a pond-frog and often lays 

 its eggs on a muddy bottom. Sometimes, however, it lays in streams, 

 and on at least three of these rather rare occasions I have found tliat 

 the eggs were attached to a hard surface, in some cases to the concrete 

 of bridge foimdations or other artificial structures. In another, the eggs 

 were firmly attached to a submerged weed mat in mid stream. In 

 one of these cases, as will be described in Chapter 9, the whole breeding 

 behaviour was modified so that actions normally taking place at the 

 surface of the water occurred right at the bottom on the hard surface, 

 and the eggs were fastened there. In other species, this sort of thing is 

 normal, but it is interesting to note the flexible behaviour of tliis 

 animal, which seems capable of adapting a whole chain of complicated 

 reactions to circumstances that are quite unusual. 



It is not only in streams that the frog may sometimes glue its eggs 

 to something sohd. I once found a single clump in a pond in an 

 unusual place, under a bush in a deep part of the pond, although this 

 pond had the shallow end that the frogs usually frequent. The clump 

 was firmly attached to a twig of a bush that was a few centimetres 

 under water. The frog must have sat on tliis twig when it laid its eggs. 

 R. sylvatica is generally considered to be nearly related to R. temporaria, 

 and, in a photograph of the eggs of tliis species, Wright and Wright 

 (1949) show them apparently glued to twigs under water. 



There are some frogs that lay their eggs out of water in nests that 

 they construct from a foamy secretion. In the description of the 

 construction of these nests, by species o£ Limnodynastes for example, it 

 is stated that the animals beat the secretion with their toes, sometimes 

 with such rapid motions that the eye can scarcely follow the move- 

 ments. In the preparation of fibrin foam, used in surgery, the clotting 

 mixture is beaten by an electric stirrer. It is surely Hkely that these two 

 procedures are essentially the same, both depending on beating air 

 into a clotting mixture. This is another instance of the existence of the 

 essential features of what appears to be most extraordinary behaviour 

 in one species in the biochemistry of a more normal species. The 

 familiar R. temporaria possesses the essential physiology and bio- 

 chemistry for making a foam nest, if it modified its behaviour in two 

 ways. It would have to lay its eggs out of water, and it would have 



