Donatpson, Law of /nunervation. 231 
The length of the line D/-D was first taken, then the 
thickness of the foot at D’ and at D. Half the sum of these 
last two measurements multiplied into the length D’—D gave the 
lateral areas of the foot, considering these as extending from 
the ankle joint to the tip of the longest toe, and twice this 
gave the areas for both sides. The length of the lines JA, 
M'B, M'' Cand M''' Ewere then taken, and the thickness 
githe, footcat Wi, 07’, A7'', M'"! and at ‘each ‘of the” toes 
A, B, Cand £ (D being omitted, as it had been already meas- 
ured). Half the sum of these two thicknesses was taken in 
each case as the average thickness of the toe, and the product 
of these numbers into the length of the respective toes, gave 
the area of the skin on one side of the toe considered as a 
plane surface. The surface is so rounded, however, that about 
one-half of the area thus calculated has already appeared in the 
surface projection of the foot, and has been counted in the 
area incluced within the original outline; therefore, intstead of 
taking this area for the side of the toes twice, it was taken 
only once. 
Thus to get the total area for the foot, there are added 
together: the two areas from the tracing—the number of 
square millimeters being determined by the planimeter—the 
area for the longest toe including that for the sides of the tar- 
sus and finally the additional areas for the four remaining toes. 
The areas thus obtained for the three frogs measured are 
given in the accompanying table, the records for the two legs 
being entered separately. 
TABLE VII. 
Giving the areas in square millimeters of the skin covering the thighs, 
shanks and feet of three frogs—R. virescens. The method of 
measurement is given in the text. 
Areas in Square Millimeters. 
— 
Frog. Thigh. Shank. Foot. 
1 Right 1584.1 1136.8 1695-3 
1 Left 1675-5 1059.0 1793 6 
2 Right 1519.2 1071.5 1539-1 
2 Left 1506.3 1035-0 1538.7 
3 Right 3177/0) 1010.9 1396.5 
2) Left 1356.2 972.4 1434.1 
Totals 9018.3 6285.6 9397-3 
