On Aquatic Carnivorous Coleoptera or Dytiscide. 183 
have attempted to make ona purely synthetical method. Linnzeus and the more im- 
mediate of his followers ‘made their classifications by a deductive or analytical 
method. Natural objects were taken for granted as forming three separate kingdoms, 
animal, vegetable, and mineral—and then each of these hypothetical or axiomatic 
kingdoms was divided and subdivided until the genus and species were reached 
and defined. This method—most useful in the early stages of scientific develop- 
ment—is being gradually replaced by an inductive or synthetic system. In other 
words species are studied and defined and then treated as units whose relations to 
one another may be exhaustively considered, This method has been clearly 
recognized by Huxley as will be seen by consulting his paragraph on morphological 
groups (“Man. Anat. Invertebrated Animals,” p. 17): and it 1s quite evident that 
only by this synthetical method can we hope to ascertain whether genera and the 
more complex aggregates have any real existence in nature, or whether they must 
yemain—as they undoubtedly are at present—merely conventional arrangements. 
On the Linnean method it may be said with perfect truth that the genera were 
made by the system, whereas it is clear that on a natural science method the system 
must be made and built up in accordance with the actual structures ascertained 
_.detail by detail. If there be an order in Nature our zoological systems must be 
made in accordance therewith, ané representative thereof; if there be no such order, 
we may then revert to the Linnwan method, for this 1s well adapted for purposes of 
artificial arrangement. At present [ scarcely think there 1s any conscientious 
naturalist who after a careful review of facts would say whether there are or not in 
Nature, independent of classifications, such things as genera. I believe, if we limit 
our view to the creatures coexisting at the present moment, no naturalist could be 
found who would venture to deny the existence of species as real and objective. 
Tt is in fact perfectly clear that the hosts of individuals livingaround us are arrangedin 
clusters or groups, isolated from other clusters or groups ; and although there may be 
and doubts as to whether certain 
doubts as to the actual number of such clusters 
masses of individuals form two isolated clusters or only one, yet no practical naturalist 
will be found who will deny the reality of the existence and isolation of such clusters, 
and it is these we call species. The nature of the connection between the individuals 
of these clusters, and the kind of isolation existing between them are most difficult 
questions, but their discussion has been commenced by Lamarck, Darwin and others; 
and these problems are now recognized as legitimate subjects for scientific investiga- 
tion, althongh perhaps but few perceive their excessively complicated and difficult 
nature. 
If, however, it be granted that species have a real existence, and if their characters 
have been well ascertained, it is clear that we may then deal with them as units to 
be classified and arranged, preliminary to considering the question whether these 
species are, like the individuals of which they are composed, arranged in naturally 
isolated clusters. This is evidently a much more complex question to deal with 
