S52 



NATURAL HISTORY. 



extremity. On the whole, the Common Frog is not an extreme frequenter of water, except 

 during the egg-laying season. 



Bell tells a story of a domesticated Frog, who came at meal-time, and snugged up to the cat in 

 cold weather ; but it must have been an exceptional Frog. Usually they can be made not to fear 

 their kind feeder, but the rising generation tease them and enjoy their prodigious jumps. Fisher- 

 men use them as bait for pike, and physiologists show the circulation of the blood in the web of 

 the foot, and Matteuchi discovered a special galvanic energy in batteries made up of their thighs, 

 so that on the whole, the Common Frog has little to thank humanity for. Bell stated that a large 

 Rana had been found in Scotland, but was doubtful whether it was a variety of the Common 

 Frog or a new species. The web of the foot forms a beautiful microscopic object, and the circu- 

 lation of the large oval blood corpuscles, and the white or colourless corpuscles, can be seen in it. 

 The species and its varieties have a great geographical distribution. 



The development of the Tadpole into the Frog has been already described, and it is merely necessary 

 to observe that the masses of eggs, or spawn, when first expelled, consist of numerous small opaque 

 globular bodies covered with a glairy substance. This absorbs a large quantity of watei', and soon 

 increases in diameter; so that the black specks, the future Tadpoles, are separated by the glairy 

 envelope one from another. The development of the young is more or less rapid, according to the 

 temperature. The embryo is at first a small spherical body, one side being dark brown and the 

 other paler. A furrow grows across the dark half, dividing it into two equal parts, and this is 

 soon afterwards crossed by another at right angles. A third and fourth furrow are produced 

 and so on, until the sphere is separated into as many granules. In the course of the 



COMMON FROG. 



