86 INTRODUCTION. 



red almost obsolete, the wings sometimes spotted, and the 

 black of the head pale. Perhaps it is a much smaller 

 bird than the average, but no one thinks of calling this 

 a " new species " ; although, if it were not for the fact 

 that there are Robins presenting every shade in color and 

 difference in size between this and the typical specimen, 

 it would certainly be a good species. Why are not the 

 same variations, which we can here see at a glance, dis- 

 covered in the other members of this family 1 They cer- 

 tainly exist. But more of this anon. 



The Robin has also characters that it bears in common 

 with other Turdince, which are its true generic characters. 

 If, then, we cannot establish a connecting link in the man- 

 ner described between one species and its nearest allies, 

 we may be sure that it never * mixes with others in breed- 

 ing, but always mates with one having the same pecu- 

 liarities as itself, although changeable to a certain point. 

 This constitutes a natural species. If, on the other hand, 

 we do find a connecting link, many times repeated in differ- 

 ent individuals, between a supposed species and its nearest 

 aUy, we may be sure that they are one. 



In the succeeding pages I have followed the classifica- 

 tion of Professor W. LiUjeborg, of Upsala, as adopted pro- 

 visionally by the Smithsonian Institution. The original 

 method being the ascending or progressive mode, while 

 the one used is the descending mode, with other minor 

 changes. 



This classification is by far the best in use, although, 

 perhaps, not perfect. By the old methods the Vulture, 

 vile feeder of carrion, was placed first, and we were told 

 to look to him as king of the birds. But King Vulture 

 has been dethroned, and in his stead reigns the Thrush 

 king over all; crowned for his sprightly intelligence and 



* The well-known exceptions to this rule are Colaptes auratm mixing 

 with C. Mezicanus; two of the Jvmcos\ and perhaps others. 



