52 
BRITISH BEETLES. 
to divide them with accuracy into any definitely 
defined groups ; if we attempt to do so, there 
will always be found intermediate forms that might 
as well be placed in one group as another : in 
classifying any section of the Animal Kingdom, or 
even the various sections of the Animal Kingdom 
itself, the difficulty will and must always be met with 
to a greater or a less degree ; “ synthetic ” forms, as 
they are called, will always be found that upset our 
preconceived ideas ; linear classification is impossible, 
and the best symbol that could be adopted for any 
classification would be a large circle with its circum- 
ference intersected and divided by smaller circles, 
which are themselves in the same way intersected 
and divided.. 
Now iu the case of the Coleoptera the difficulties 
are increased by the enormous amount of material 
already known, as well as by the new forms that are 
being continually added ; any arrangement must 
therefore be regarded as, in the present state of our 
knowledge, unsatisfactory, artificial, and provisional, 
and every defined group must be allowed to contain a 
certain number of exceptions. 
The system of Latreille, founded on the number of 
the joints of the tarsi, has been the one which has 
perhaps, up to recent times, been most generally 
adopted j under this system many allied families, the 
most fully developed, possessing five joints to all the 
tarsi, have been termed the Pentamera; those with 
five joints to the front and middle legs, and only four 
to the hinder, Heteromera ; those with apparently only 
four to all the tarsi, Tetramera ; and those with 
apparently only three to all the tarsi, Trimera. 
