HOW TO USE THE KEY. 



53 



SECT. IV. Directions. — now to use the key. — now to measure a 

 specimen, etc. 



1. how to use the key. 



§ 92. We have iu 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 aflbrd. 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 arljitrary 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 ))efore and two lichind. It therefore comes 

 under the third division (HI). Turning to III, we read : — 



Bill witli a cere, and strongly eplgnathous, 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 stifi' 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, etc., Picus, 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. Thus 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 framin 

 the key. After each determination, either the name of a genus is encoua 

 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 



to 



