20 On the present state of Zoology. 
himself can distinctly appreciate ; that, at any rate, points, with respect 
to which there exists any ground for difference of opinion, can hard- 
ly be advanced in proof of a theory, whatever there may be to render 
that theory probable. 
In fact, we believe the time is not yet come, in which it is possible 
to demonstrate the truth of any theory whatever. We may shew the 
apparent influence exerted by certain principles which seem capable of 
being- deduced from the data already in our possession ; but we con- 
ceive that we must be more acquainted with the structure and affini- 
ties of animals, before we can establish such principles upon a sure 
basis. Nevertheless, we would not discourage persons from making 
the attempt. We are rather inclined to let all naturalists hold their 
own opinions on this subject, convinced that truth will work its way 
in the end, and that, if not found in exact agreement with what they 
had anticipated, it will at least have received some light from their 
researches. 
In the meanwhile, those who keep aloof from speculations of the 
above kind should endeavour to enlarge the bounds of our positive 
knowledge as regards this science. Let them investigate some of 
those departments, to which so little attention has been as yet given, 
and try to place the several ramifications of the great system of na- 
ture upon a more equal footing. By so doing, they will supply sound 
materials for such as choose to speculate upon the exact plan on which 
that system is constructed, at the same time that they help the science 
forwards to that point, which, when arrived at, the plan will in some 
measure develop itself. For it should be remembered, that there are 
two distinct objects to be attained, as regards the natural system : 
" first, the arrangement of all animals according to their true rela- 
tions ; and then the discovery of those general principles (assuming 
that there are such) by which these relations are governed."* Now 
had we already effected the first of these objects, which can only be 
the result of a rigid analysis, extended to all the groups of animals 
with which we are acquainted, we should probably have little difficul- 
ty in evolving the latter. At present, however, this has been but 
very imperfectly done. And, perhaps, we are more likely to proceed 
rightly in this matter, when we go to work unfettered by any theo- 
retical views, which in our anxiety to uphold, we are liable to have 
our judgment biassed to a degree to which we ourselves are totally 
unconscious. It is, undoubtedly, at all times agreeable to true philo- 
sophy to ascend by inductive reasoning from known facts to general 
* The above passage will be found nearly similar to what Mr Swainson has 
expressed at p. 200 of his Preliminary Discourse. 
4 
