166 
the first, and is the sort so often seen on is- 
lands, on mountain peaks or other isolated con- 
tinental areas; and it is this that seems to be 
at present the debatable kind of intergradation. 
Shall this be considered equivalent to uninter- 
rupted continental intergradation, or shall it 
be ignored entirely as intergradation, and the 
forms so limited be considered distinct species, 
although some of their individuals may not be 
distinguishable from those of some other 
form ? 
The recent remarks of Mr. H. S. Swarth 
on the subspecific relationships of certain jays 
of the genus Aphelocoma? again brings up this 
question. A statement of this particular case, 
which the present writer has already briefly ex- 
plained,’ may be of interest in the present 
connection, since it is typical of the third kind 
of intergradation. Aphelocoma californica cali- 
fornica, Aphelocoma californica immanis, and 
Aphelocomacalifornica hypoleuca are three jays 
occurring on the Pacific coast from Oregon to 
southern Lower California, the first two with 
continuous ranges, the third supposedly iso- 
lated. Adjoining Aphelocoma californica im- 
manis on the eastern side of the Sierra Nevada, 
and living sometimes at the same localities, 
where apparently specifically distinct,is A phelo- 
coma californica woodhousei. The last, how- 
ever, ranges eastward to Texas, where it inter- 
grades with Aphelocoma californica texana, 
and through other Mexican subspecies with 
Aphelocoma californica sumichrasti of south- 
ern Mexico, the range of which is entirely sep- 
arate and far removed from any of the races 
of California or Lower California. Some in- 
dividuals of Aphelocoma californica sumi- 
chrasti, however, are difficult, if not impossible, 
certainly to distinguish from A phelocoma cali- 
fornica immanis or Aphelocoma californica 
hypoleuca. 
Mr. Swarth would consider that the individ- 
ual variation of Aphelocoma californica sumi- 
chrasti from southern Mexico, which bridges 
the difference between A phelocoma californica 
2Uniw. Calif. Publ. Zool., XVII., No, 13, Feb- 
ruary 23, 1918, pp. 406-413; 420-421. 
3 Condor, XIX., May, 1917, p. 94. 
SCIENCE 
[N. S. Vou. XLVIII. No. 1233 
immanms and Aphelocoma californica hypo- 
leuca, is not intergradation in a subspecific 
sense; furthermore, he regards Aphelocoma 
californica hypoleuca from southern Lower 
California as a distinct species (although he 
admits that certain examples of Aphelocoma 
californica tmmanis found in northern Cali- 
fornia are indistinguishable from this Lower 
California form) because of the interposition 
of a darker form of Aphelocoma californica, 
the range of which he considers widely re- 
moved, and with which he supposes A phelo- 
coma californica hypoleuca does not geograph- 
ically intergrade.* In such cases the inter- 
vening form has the same biological effect as a 
land or water barrier. Thus the particular 
point brought out is that intergradation by in- 
dividual variation is not intergradation in a 
subspecific sense, and that, therefore, a form to 
be a subspecies must have a continuous range 
and merge geographically. With this as the 
only criterion, all island and isolated alpine 
forms must be considered distinct species, how- 
ever slightly and inconstantly they may be 
differentiated, a view by no means’ held by 
zoologists generally. 
The principle underlying the use of inter- 
gradation as an indication of subspecific re- 
lationship and sought to be expressed in no- 
menclature by a trinomial is that a subspecies 
is an imperfectly segregated species. Mani- 
festly no form that is a geographic representa- 
tive of a species is perfectly segregated if any 
of its normally adult individuals are practic- 
ally indistinguishable from comparable indi- 
viduals of another form. We should, there- 
fore, make our nomenclature conform to the 
facts, not our facts to the nomenclature. In 
order to do this and satisfactorily to settle the 
specific status of a numberof closely related 
forms that collectively cover a large geographic 
area, it is important that we take not only one 
or two contiguous, but all the forms and their 
4 That Aphelocoma californica hypoleuca, as we 
shall elsewhere explain, proves to have a range 
practically continuous with Aphelocoma californica 
californica and completely intergrades geograph- 
ically with the latter, does not affect the principle 
at present involved. 
