1891.] NEW YORK ACADEMY OF SCIENCES, 81 
able habitats—although known torun into something else; or was 
there a still better way of expressing such important biologic 
facts ? Here wereevidently recognizable stages in the process of 
evolution by environment. How were they to be recognized so as 
to be made use of in philosophical biology ; in what way could 
they be chronicled in descriptive biology ? That many of these 
intergrading forms possessed noteworthy differences is evident. 
from the fact that they formerly held the rank of unquestioned 
species. 
For a time a wavering course was followed, some writers lump- 
ing as one species all forms that seemed to intergrade, while 
others continued to recognize all of the more prominent phases 
as species. Soon after it became the fashion to distinguish them 
as varieties, under what may be termed a qualified quadrinomial 
system of nomenclature. Thus our Eastern red squirrel, or 
chickaree, was called Sciuwrus hudsonius; its Rocky Mountain 
representative, or Fremont’s chickaree, became Sciwrus hudso- 
mius, var. fremonti ; another Rocky Mountain form, known as 
Richardson’s chickaree, became Sciurus hudsonius, var. rich- 
ardsoni; a Northwest coast form, known as Douglass’ chickaree, 
became Sciwrus hudsonius, var. douglassi ; and so on in all sim- 
ilar cases. This proved a cumbersome method, and soon the 
term ‘‘ var.” was dropped, resulting in a trinomial name, pure 
and simple, for the designation of swdspecies. ‘This in reality is 
the binomial system of Linné in spirit, modified slightly in the 
letter to fit what was an ideal system of nomenclature at the 
time of its inception, to the requirements of modern biology. 
Hence American mammalogists adopted, in common with orni- 
thologists, trinomial designations for nascent species, reserving 
the binomial distinctively for species in full standing. This 
system became generally current about 1883. 
The several geographic, intergrading forms of a wide-rang- 
ing species often differ more from each other in their extreme 
phases than do, in other cases, perfectly distinct species. Hence, 
through the use of trinomials, two important things are accom- 
plished: first, a means of distinguishing two kinds of relation- 
ship among congeneric forms, the use of a binomial name in- 
dicating entire distinctness, without regard to kind or degree 
of difference, while the use of a trinomial implies known in- 
tergradation, notwithstanding the very wide difference which 
frequently exists between the extreme phases of a group of inter- 
grading or conspecific forms; secondly, provision for a conve- 
nient and tangible way of giving expression, by means of a definite 
formula, to some of the most suggestive facts in the evolution 
of life. It is not claimed that this is a perfect system of nomen- 
