7 
general relationships between various species. They are a necessity for 
international scientific intercourse and familiarity makes them much less 
forbidding than they seem at first. The ease with which such scientific 
names as geranium and hippopotamus, to say nothing of Junco and Vireo, 
have glided into popular usage shows that they are not as difficult and 
awkward as they appear on paper. 
The present binomial system of nomenclature was introduced by 
Linnaeus, the great Swedish botanist, and embodied in his “Systema- 
Naturae,” tenth edition, 1758, which is the authority accepted by American 
ornithologists. In this system each species is given a double name, the 
first term being that of the genus to which it belongs, the second that of 
the species. Generic names are not duplicated within the sphere of zoology 
nor are specific names within the genus. Thus, the American Robin is 
Planesticus migratorius, that is, that species of the genus Planesticus 
which is named migratorius. Other species of Planesticus have other 
specific names. 
The three objects of scientific nomenclature are exactitude, univer- 
sality, and permanence. To this end the naming of zoological material is 
subject to strict laws whose principles are universally accepted and applied 
according to strict codes. Under these laws the scientific name of a species 
is not a matter of personal preference, but is fixed, so that few or none can 
dispute it, and no changes can be made in scientific nomenclature except 
such as are necessary to correct current mistakes in the application of the 
laws of the code. With increased knowledge it has become necessary to 
depart slightly in letter, though not in spirit, from the strict binomial 
system of Linnaeus, and by adding a third term as name of the subspecies 
to make it a trinomial one. Wherever a three-term name is used, it is 
that of a subspecies of the original binomial form. The first specimen 
described, or the first specimen to which a name has been attached, is 
regarded as the so-called “Type” form. Therefore, in dividing a species 
into subspecies the form which was first named as a species is automatically 
given precedence and its subspecific name is formed by a repetition of its 
specific name. Thus the American Robin that was first described and 
specifically named by Linnaeus in 1766 as migratorius , when mentioned 
subspecifically in distinction from the Southern Robin or the Western 
one becomes Planesticus migratorius migratorius. The Western Robin, 
first separated from it by Ridgway in 1877, was named by him as Planes- 
ticus migratorius propinquus, and the Southern Robin by Batchelder, in 
1900, is Planesticus migratorius achrusterus. In practice, where the 
generic or specific names are evident from the context, it is customary to 
indicate them by initial, as P. migratorius , or P. m. migratorius. 
GEOGRAPHICAL DISTRIBUTION 
The broader facts of the geographical distribution of life are patent 
to the most casual observer. The primary divisions of distribution, the 
Tropics, Temperate, and Arctic zones, are obvious, but closer study shows 
that within these broad divisions minor and less obvious ones can be 
detected. In America, north of the gulf of Mexico, there are three life 
regions, roughly following the above, called the Tropic, the Austral, and 
the Boreal. These are subdivided into life zones each characterized by 
its own peculiar assemblages of plants and animals. 
