| ia ig 
HOW TO USE THE KEY. 53 
SECT. IV. Directions. —HOW TO USE THE KEY.~—HOW TO MEASURE A 
SPECIMEN, ETC. 
1. HOW TO USE THE KEY. 
§ 92. We have in hand a bird which we know nothing about, and desire 
to identify; that is, to discover its name and position in the system; and to 
learn whatever else the present volume may afford. Let us suppose it to be 
that little black and white spotted bird which we often see climbing about 
our fruit trees, boring holes in the bark. 
The Key opens with an arbitrary division of our birds, according to the 
number and position of their toes. Our specimen, we see, has four toes, 
arranged in pairs; that is, two before and two behind. It therefore comes 
under the third division (III). Turning to III, we read :— 
Bill with a cere, and strongly epignathous, etc., 
— not cered; inner hind toe with 3 joints, etc., 
—only 2 joints. (f) 
We see that the bill of the specimen is neither cered nor hooked, and 
that the inner hind toe is 2-jointed. Following, therefore, the reference- 
letter (f), we find three alternatives, viz., 
(f) Tail of 8 feathers, etc., 
— 10 soft feathers, etc., 
— 12 (apparently only 10) rigid acuminate feathers. (g) 
The tail feathers of the specimen are stiff and pointed, and we count ten 
perfect ones, besides a rudimentary pair concealed at the bases of the others. 
Evidently, then, we continue with the reference letter (g¢), as follows :— 
g) Birds > 14 inches long, etc., 
(g) Birds <14 in.; ridges on upper mandible reaching tip, ete., . . . . . Prcus, 131. 
The specimen is much-less than fourteen inches long, and the sharp ridges 
on the sides of the upper mandible run quite to the end of the bill; and 
here, at last, instead of a reference-letter, we find a genus named; which 
is the one to which the specimen belongs. The bird is a Picus. 
§ 93. Tuus the key conducts to a genus, by presenting in succession, 
certain alternatives, on meeting with each of which, the student has only to 
determine which one of the two or more sets of characters agrees with those 
afforded by his specimen. There will not, it is believed, be any trouble 
in determining whether a given character is so, or is not so, since only the 
most tangible, definite, and obvious features have been selected in framing 
the key. After each determination, either the name of a genus is encoun- 
tered, or else a reference-letter leads on to some new alternative, until by a 
gradual process of elimination the proper genus is reached. After a few 
trials, with specimens representing different groups, the process will be 
. shortened, for the main divisions will have been learned; still, the student 
