184 Gn Aquatic Carnivorous Coleoptera or Dytiscide. 
than that of species; but if we suppose it to be answered in an affirmative sense,. 
we may then treat these complex aggregates as themselves units, and study them 
in the same way as we have supposed to be already done in the case of genera and 
species. Looking at taxonomy in this aspect, species are the units of the classifier, 
genera are ageregates of the first degree, groups of genera aggregates of the second 
degree, and so on. 
Whatever view be taken as to the nature of genera, it will at least be admitted that 
there does not prevail among naturalists at present so great concord as to their 
limits, as that which we find to exist about species. It is undoubtedly the case 
that an attempt to define genera in a thoroughly natural manner is much more 
difficult than the study of species; while an additional obstacle is thrown in our 
way by the fact that we are not yet acquainted with all existing species, so that 
any day by the discovery of a new and intermediate form two apparently distinct 
genera may be connected together. 
This process of forming genera by synthesis—by the accord existing between 
species as to the whole of their characters other than specific—has notwithstanding 
its difficulties progressed in a more or less recognized manner, and is no doubt 
destined to supplant completely the process of artificial classification ; and there can 
I think be but little doubt that the perfection of the method will be, for a while at. 
any rate, accompanied by an increase in the number of primary aggregates recognized 
by zoologists. The enormous increase that has already occurred in the number of 
genera has occasioned much discussion and given rise to considerable complaint 
against those who make new genera; and in point of fact the history of systematic 
zoology presents us with a picture of constant protest by the older naturalists 
against the multiplication of genera by their younger fellows. And it must be 
admitted that the increase has indeed been enormous ; Linnzeus only admitted 354 
genera as composing the whole animal kingdom (‘Systema Nature,” Ed. xii); the 
nuuber at present recognized could not be readily ascertained, but it is something 
enotmous ; there are I believe about ten thousand genera recognized merely among 
the beetles, and I anticipate that this number will increase to forty or fifty thousand. 
I do not myself feel alarmed at this extraordinary multiplication, but there is one 
point connected with it that is certainly to be regretted ; it is the corresponding 
increase in the number of generic names; the enormous growth in this respect has 
already brought us to the unfortunate pass that few of us, even though we are 
specialists, recognize, much less understand, the generic names even of the depart- 
ment to which we have given particular attention ; and thus the names of genera 
come to have but little value. Seeing then how uncertain are the limits of genera 
ai present, and how doubtful it is what kind of relation the genera we now adopt may 
bear to those of the future when systematic zoology shall have assumed a more 
periect form, we may well consider whether some method cannot be devised to 
limit the increase of generic names, or at any rate to render their recognition a 
