380 



LAND ANIMALS 



specimens. 8 Keeping various species of birds in a more moisture- 

 saturated air led to a darkening of the plumage. The thrush, Hylocichla 

 mustelina, or the Inca pigeon, Scardafella inca, afford examples. 9 

 Such animals approach varieties that are found in regions with a moist 

 climate. The weaver finch, Munia flaviprymna, from the Australian 

 desert, after a captivity of three years in the damp climate of Eng- 

 land, assumed a coloration of its plumage that shows agreement with 

 the related but not desert-dwelling species, M. castaneithorax, in color 

 pattern as well as in the deeper tinge (Fig. 109). 10 



Observation corroborates these experiments. Mountain and northern 

 butterflies display much darker scales; however, this may be due more 



Fig. 109. — a, Australian weaver-finch, Munia flaviprymna, a desert inhabitant; 

 b, the same after three years' residence in a humid climate; c, Munia castanei- 

 thorax, not a desert form. After Seth-Smith. 



to temperature than to humidity. The darkening of the red slug 

 (Avion empiricorum) is said to parallel the humidity; in the same 

 manner certain snails, Helix arbustorum and Succinea pfeifferi, are 

 darker than usual in damp habitats. 11 On the other hand, an abundance 

 of moisture seems to promote the existence of albinistic snails. The 

 common frog (Rana temporaria) and the mountain lizards (Lacerta 

 vivipara) are also said to be darker in a more humid environment. 

 The song sparrow is paler in the arid parts of the United States, and 

 more melanistic in the wet Puget Sound country, than it is in the mesic 

 regions of the eastern states. This reaction is widespread among the 

 mammals, without being, however, a universal phenomenon. Thus the 

 water-inhabiting varieties of the field mouse, Microtus terrestris, the 

 so-called water rat, are generally darker colored than the garden- 



