4, heed ON SYSTEMATIC ZOOLOGY. 
by a totally different process of investigation, arrived 
at the same general result ; but with this difference,—that 
he discovered properties, which belonged to this series, 
of universal prevalence in natural groups, and he deter- 
mined several of those laws which regulated the variation 
of animals; a process of induction which heretofore 
had never been dreamed of. These discoveries let in 
a flood of light on the study of nature, and converted 
that which hitherto had been a science of observation 
into one of the deepest philosophy. In such a new and 
untrodden field, it would have been strange indeed, if 
- subsequent researches had not detected errors. Our 
surprise, therefore, is, not that this theory should be 
partially defective, but that it should develope so much 
that is to endure so long as science is cultivated. The 
system of Mr. MacLeay is eminently natural ; although, 
as he himself. repeatedly declares, it does not claim to 
be the natural system; meaning thereby, we may pre- 
sume, that many principles of that system, and many 
properties of natural groups, were unknown to him. 
This admission, on the part of the master, should be 
borne in mind, when reading the commentaries of his 
disciples ; for it has unfortunately happened in this, as 
in other instances, that the reputation of this eminent 
naturalist has suffered much more from the zeal of his 
admirers than from the hostility of his adversaries. On 
a careful consideration, therefore, of the principles of 
natural arrangement developed by our author, they may 
be all comprised under one or other of the following: — 
1. The demonstration of the circular nature of affinities 
in natural groups; 2. The component parts of every — 
group being regulated, in their variation, by some de- 
finite number ; and, 5. ‘The system of representation, by 
which the contents of one natural group are represented 
analogically by the contents of other groups. This . 
last law, indeed, was not suspected to be universal ; but 
merely confined to one in every fifth group. The 
theory of analogy and affinity comes also under this 
latter head ; being, in fact, one of the tests or proofs to 
