252 AN UK A CHAP. 



season these pads are enlarged into cushions covered with black 

 horny rugosities. 



The iris is golden, with dark specks. The coloration is, 

 generally speaking, brown above, with black-brown irregular 

 spots, especially on the sides of the body, and with cross-bands 

 on the legs. The under parts of the male are white or pale 

 yellow, with a bluish tinge on the throat, while the female is 

 more yellow instead of white, inclining to orange. In both sexes 

 the under parts are mostly spotted with darker colours. A large 

 dark-brown patch, extending from behind the eye over the 

 tympanum towards the shoulder, is always present and has given 

 this frog its specific name. Otherwise the coloration varies con- 

 siderably ; more or less according to the locality and nature of the 

 surroundings, and to individual variation and temporary change 

 of colour. 



Some specimens are almost spotless above and of a rich 

 brown, or almost yellow colour, the spots being restricted to the 

 sides below the lateral folds. Others have very few spots, but 

 these are then arranged in two interrupted streaks on the 

 back. The under parts, especially the flanks, may be lemon 

 yellow instead of whitish, and the darker markings may be 

 almost absent. Boulenger has figured a beautiful specimen, 

 almost orange red, with red spots and vermiculations on the yellow 

 under surface. I have found similar red specimens of unusually 

 striking appearance between Berlin and Spandau in a forest- 

 glade, through which run little streams with banks of red ferru- 

 ginous soil. Specimens which live in woods with rich black soil 

 are often very dark, all the brown and reddish tints being absent. 

 The variations are, however, really endless, and it is difficult to find 

 two individuals exactly alike, even amongst a great number collected 

 in the same locality. Moreover, they change colour. Warmth 

 makes them paler, cold causes the chromatophores to expand and 

 the whole frog appears darker. During the breeding season the 

 males assume a delicate bluish hue, especially on the throat, but 

 this film quickly fades away when they are taken out of the 

 water. It is caused by the swelling of the cutaneous lymph- 

 spaces which extend their ramifications into the epidermal layer, 

 and it is not a question of pigmentation or of chromatophores, 

 but a case of interference -colours, blue being frequently the 

 result of the light passing through a cloudy, colourless, but not 



