Animal Behaviour 



shalled into definite arrangement, and those frogs in which the 

 arrangement was such as to be helpful in hiding them in their 

 environment were missed by enemies, while others were destroyed. 

 The protective arrangements were inherited and again emphasized 

 through generation after generation until we have in the Salientia 

 of to-day animals wellnigh invisible in their haunts. When we 

 do see them against their background of water and foliage, it is 

 wonderful how greatly the elongated spots and horizontal bands 

 of light and dark that make up the pattern on the back and that 

 cross the folded legs resemble the alternating sunshine and 

 shadow made by the sun shining between plant stems and grass 

 blades. The light-edged rounded spots of Hyla gratiosa and 

 Rana pipiens are marvellously like the shining sun-spots that 

 dance on the ground when sunlight is streaming through dense 

 foliage. 



One of the most complicated conditions exists in the cases 

 where a given pattern is vividly displayed when the frog wears 

 a dress of some medium shade and is wholly obscured in the 

 light and dark phases of colouration. This is true of the colour 

 pattern of Acris gryllus, Smilisca haudinii, Hyla gratiosa, Hyla 

 versicolor, and others among the Hylidae, and of Rana caieshiana, 

 Rana grylio, Rana onca, and perhaps others among the Ranid^. 



The origin of the colour of Salientia is still a problem. It is 

 largely a chemical problem, closely connected with the food of 

 the species and with the conditions of the chosen environment. 

 The pigments are thought to be mainly excretory in origin, waste 

 products deposited in the skin — perhaps through the influence 

 of light and heat — instead of disposed of in the ordinary fashion. 

 The white pigment is thought to be guanin, related to uric acid, 

 and the metallic pigments are named from their composition 

 "guanin cells" or " iridocytes." 



XL Animal Behaviour 



" How intelligent is the creature?" is a question of interest 

 in the study of any animal. How many of its actions are the 

 result of automatic response to the various stimuli of the environ- 

 ment? How many can be explained wholly as instincts, that is, 

 racial habits inherited through a long line of ancestry and per- 

 formed alike by each and every member of the race? How many 

 actions denote intelligence higher than this? 



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