NO. 1158. ■ VARIATIONS OF HTLA BEGILLA—TEST. 489 



there is considerable variation in this, as in all else, still the diminution 

 is very marked as a rule, in some cases being not much more than is 

 found in some species of Ghorophilus. This has been naturally brought 

 about to some degree by the scarcity of water in a part of the range 

 and by the diminished vegetation which accompanies and is implied by 

 the lessened moisture. Where trees and shrubs exist, as in the higher 

 altitudes of middle and southern California and N'evada, as distin- 

 guished from the lower valleys and deserts, and in northern California, 

 Oregon, and Washington, regilla tends to become more arboreal, but it 

 is generally terrestrial in its habits, resembling, as said before, Hyla 

 picTceringii, in being chiefly found about ponds, springs, and like moist 

 localities. This may account for the size of the digital disks being 

 reduced to a greater degree than is the webbing between the toes, for 

 though the arboreal life might be only rarely possible, the opportunity 

 for swimming would more frequently present itself. 



As would be expected, then, the greatest reduction is usually found 

 in the desert region, the webbing increasing toward the north and with 

 rising altitudes. In spite of the indication, however, that with higher 

 altitudes go more webs, ]N^os. 20190-203, from Santa Isabel, at an 

 altitude of some 1,500 feet, in the mountains of San Diego County, 

 have the smallest webs and disks of all examined. The specimens 

 were fresh, collected considerably less than a year before they were 

 examined, and were in perfect preservation, so that the reduction is 

 natural, and not due to shrinkage in the alcohol. The web (fig. 8), 

 starting from the base of the first phalanx of the fifth toe, swings back, 

 but is attached to the fourth toe at the joint between the second and 

 third phalanges. Sweeping back from a corresponding point on the 

 opposite side of the toe, it is brought forward again to the joint between 

 the first and second phalanges of the third toe, and starting from a 

 little back of the end of the second phalanx, it is attached midway the 

 first i)lialanx of the second toe. From near the joint of the first i>halanx 

 it then goes to a like point on the first toe. This small amount of 

 webbing is also found in specimens from Santa Barbara and Sonoma 

 County, and the disks are correspondingly lessened. 



But in specimens from Johnson and Surprise canyons, Panamint 

 Mountains (altitude 6,000 feet), of even more arid character than Santa 

 Ysabel, the webbing reaches its maximum (fig. 9), connecting the bases 

 of the disks on all the toes, though the last phalanges of all except the 

 fifth are merely widely fringed. In no other specimens do ao much web 

 and so large disks occur. 



The usual webbing, however, of middle and southern California and 

 Nevada, though like the specimens from Ysabel in other respects, differs 

 in that the webbing runs up both sides of the fourth toe to the middle 

 of the second phalanx. This degree is also found in Cape St. Lucas 

 specimens, and, only slightly increased, in those from Lake Tahoe, 

 though these show the change toward the northern type. 



The invariable condition north of California, and which occurs also in 



