/ 



Hylidae 



may oe very large, extending well up on the eyelids, and sending 

 a point far back on the neck, or it may be decidedly small. It 

 may be of solid colour, or only in outline. It may be separate 

 or connected with the band in the midline of the back, or it may 

 be broken into two or occasionally three spots. The longitudinal 

 bands of the back may be distinct broad bands, two, three, or 

 occasionally five in number, or they may be broken into spots 

 rounded or elongated, regular or irregular in shape. The bands 

 may have parallel sides, or may be fantastic in shape. They may 

 be broad and conspicuous, and if there are spots instead of bands, 

 these may be many and crowded, or bands and spots may be so 

 reduced that they are scarcely noticeable. 



Judging from the one hundred fifty specimens examined 

 from regions about San Diego and San Francisco, California, and 

 Seattle, Washington, those from the south are more likely to have 

 the dark colour in lines or bands with few spots between and on the 

 sides, and those from the north to have broken bands and crowded 

 spots showing much more dark colour. The specimens from the 

 north, besides having more dark colour, measure considerably 

 larger than those at the south. 



Hyla regilla has the power to change colour rapidly. Let us 

 isolate two and observe them. They have been in wet moss in a 

 dark place, and are nearly black in colour. When looked at more 

 closely, one is seen to be a very dark green, and the other a rich 

 dark brown. There is no trace of spots; only the light band 

 above the jaw shows. On exposure to bright light, the colour 

 immediately lightens; one becomes decidedly green, the other 

 decidedly brown. Soon a pattern of spots and bands shows 

 obscurely on their backs. This pattern becomes more and more 

 distinct as the background grows lighter. When the medium 

 shade of green or brown is at its brightest, the pattern shows 

 most vividly. However, if they still continue to remain in bright 

 light, we could scarcely find time to draw the pattern while it is 

 vivid, for as the background continues to grow light, the spots 

 begin to be dulled. They become less and less distinct, the back- 

 ground becomes still more light in tone, and the pattern wholly 

 fades, and leaves one frog metallic fawn colour with golden reflec- 

 tions, and the other yellowish green of a very light tone. This 

 change from a colour so dark that there are no spots to a light 

 unspotted colouration may take place within eight or ten minutes. 



136 



