TAVERNER — TEST OF THE SUBSPECIES 127 
the forms concerned. The accidental absence of intergrades in these 
cases complicates the demonstration but cannot alter the fundamental 
facts. No system of classification has ever entirely done away with 
the necessity of exercising some judgment and probably none ever will, 
and the best we can arrive at is to reduce the human equation to its 
lowest possible terms consistent with the facts of nature. The pos- 
sihility of intergradation where contact between races is physically 
impossible must necessarily be estimated under the guidance of what 
evidence we have. The test of intergradation or its possibility where 
physically prevented gives a far more definite basis of judgment than 
unmeasurable generahties expressed as vague comparatives of difference. 
That such proceeding does in practice and in some cases, approximate 
the criterion laid down by Doctor Merriam is beside the point as the 
resemblance is superficial and not fundamental. In one case it is 
frankly an expedient, a suggestion or means to an end, in the other 
it is the end itself and final. 
In this argument I do not forget such cases as the hybrid flicker nor 
Lawrence’s and Brewster’s warblers. These if anything substantiate 
the view that degrees of sterihty form the specific boundary lines. That 
the parent forms of these anomalies are not mongrelized is evidence 
that such cross breeding is under a handicap as against purer lines of 
descent; for it is a mere matter of mathematics to prove that otherwise 
species that hybridize regularly, even if only occasionally, would even- 
tually merge. I have little doubt that the hybrid flicker which shows 
no appreciable evidence of sterihty is only continued through fresh 
crossings of original stock and that should either parent form be ex- 
terminated, it would in a few generations die out through inherent 
weakness and inability to compete with either of its more virile parent 
forms. 
Therefore, for reasons of both expediency and philosophy, stability 
of nomenclature and the teachings of evolution, I respectfully submit 
that the fact of intergradation is the only proper and workable test 
of subspecific status and should be firmly held to by all students of 
speciation. 
JOURNAL OP MAMMALOGY, VOL. I, NO. 3 
