THE COMMON FROG. 53 



with a brownish, reddish, or yellowish tinge, according to its 

 surroundings ; because a frog changes its colour. There are, how- 

 ever, some distinctive marks which are always apparent. The 

 long black spot behind the eye, rendered still more conspicuous 

 by the light line immediately under it gives character to the head. 

 The thighs are striped, the belly is much lighter and spotted, 

 otherwise we can scarcely affirm that a frog is brown, or green, or 

 yellow. When just emerging from the mud it is so dark that the 

 black spot is scarcely seen, and when among grass or plants the 

 tint is greenish. These changes were always observable in my 

 little Batrachian family, and they were very frequent. One little 

 frog that liked to keep above and in the light was of a golden 

 tint, and the others that preferred hiding were much darker ; and 

 though all changed their tints, each was, under all circumstances, 

 sufficiently distinct for me to recognise it. The change of colour 

 is protective. Not that we may suppose that a frog deliberately 

 resolves to turn brown or black on dark ground, or green when 

 in the grass, but that there is something in the colour of 

 contiguous objects which does act upon the skin is very certain. 

 Claus tells us that " the colourings of its skin are due to pigment 

 cells in the cutis, and that the changes of colour are caused by 

 changes in the form of the cells." 



It is evident, therefore, that an external influence, and not a 

 voluntary operation, acts on the cells ; though the terms " imita- 

 tion " and " mimicry " have been used in describing changes of 

 colour in some insects and birds. The skin of a frog is also 

 richly supplied with nerves, and is to be regarded as the seat of 

 the tactile sense. A larger and older frog, in its second summer, 

 gave me frequent opportunities of remarking its extreme sensitive- 

 ness, starting at any sudden or jarring sound, as a nervous person 

 starts at a gun going off, or a door slamming. This frog, known 

 as " Froggin " (while the very young ones were " Froggies "), had 

 the run (or jump) of a glazed off-shoot to our house, called in the 

 house-agent's advertisement "Conservatory." In this little 

 fabrication, however, in company with a toad, Froggifi seemed 

 well satisfied. He had his favourite corners from which he . 

 surveyed the world, one most frequently chosen being a.- damp 

 nook almost under a water-tap. There was a fissure between the 

 bricks in that corner into which he backed himself, and as he 

 grew bigger edged himself sideways into it, with much perse- 

 verance, but with little apparent comfort, until he outgrew it 

 beyond any further squeezing, but did not even then desert the 

 corner. Drippings from the tap and even a good sprinkling he 

 seemed to regard as a refreshing summer shower ; but if a rush 



