272 
Mr Bernard, On the Unit of Glassification 
formula will be found adequate. But it is now a question of 
how best to carry out this indispensable preliminary sorting. 
The higher orders are apparently fairly easy to sort out, and 
being comparatively few in number, errors are lightly corrected. 
But it is when we come to finer subdivisions, and have to dis- 
entangle the ultimate twigs of the tree of life, that the difficulties 
become almost insuperable, and if we are to attempt it, it behoves 
us to work according to the most accurate and methodical system 
we can devise. 
Now in all sorting-out processes it is obvious that we must fix 
upon a unit. We must then select these units and lay them 
together in groups, and these groups again into groups of a higher 
order, and so on. Hence the first question which confronts us is, 
What unit shall we adopt for our attempts to classify the organic 
world? The case is of course a specially difficult one because the 
variations are so multitudinous, and of so many different degrees 
of value, vast numbers being excessively minute. But the more 
difficult it is the more perfect our technique must be. The very 
first step we can take towards this perfection of our technique 
is to see that our units have some actual demonstrable existence, 
and the next that they can be fairly accurately defined. Unless 
these conditions are fulfilled one would fancy that all our 
attempts at sorting were but waste labour. 
Now with this insight into the needs of the case it is not 
difficult to see why the Linnean system, however excellent it may 
be as a formula for a natural classification when we have worked 
such a classification out, is useless as a technique for the work 
itself. Its unit is no longer even approximately definable, it is 
in fact one of the very divisions which we wish to discover, and of 
all the divisions that one which is the most difficult to discover. 
I refer to the ideal genetic group called ‘species,’ which is the 
unit of classification under our present system. Borrowed at first 
as the fixed created species of the theologian and of common 
observation, these species have served as the most natural units 
to be marshalled into genera and so on. It is true that varieties 
early came in as difficulties, so slight however as to be negligible. 
So long as we believed in fixed species, they could be regarded as 
accidental appendages of one kind or another which did not 
affect the existence of the unit. The species was the funda- 
mental fact. 
It is not uninteresting to enquire why, so long after we all 
recognise that there is no such thing as a fixed species, and that 
all is in a state of flux, we have not altered our unit. I explain 
this as due to the fact that universal variability has been regarded 
too theoretically. In practice it may be argued we see only what 
our fathers saw, that is, fixed species. In practice, therefore, there 
