184 Mr. H. E. Strickland on the Natural System 
6. Henricia, Gray. Linckia, Forbes not Nardo. 
The rays 5, rounded, tapering, with rounded tubercles near the 
ambulacra; the dorsal wart obscure, few rayed, often hidden with 
small spines. 
1. Henricia oculata, Gray. Asterias oculata, Penn. Asterias 
seposita, Penn.? Rays 5, closely reticulated with small spines. 
Inhab. European Ocean. 
[To be continued. | 
X XIII.— On the true Method of discovering the Natural System 
in Zoology and Botany. By Hueu E. sles ees M.A., 
F.G.8., &c.* : 
Ir is probable that most naturalists at the present day have an 
instinctive belief in the existence of a natural system in Zoo- 
logy and Botany, but there are very few who if questioned on 
the subject could give any clear explanation of the grounds of 
their belief, of the nature of that system, or of the mode by 
which a knowledge of it may be attained. The uncertainty 
which hangs over the subject is doubtless owing to the ob- 
scure and metaphysical nature of some of the principles in- 
volved, and still more to the vague conceptions and crude 
theories which have been promulgated on the subject. 
This essay is contributed in the hope that, even if its own 
arguments are of little value, it may, at least, induce others to 
investigate the subject on more correct principles than have 
hitherto been followed. 
The postulate with which I commence the i inquiry is, to let 
it be granted that there are such things as species, distinct in 
their characters and permanent in their duration. This being 
admitted, we define the natural system to be the arrangement 
of species according to the degree of resemblance in their essen- 
tial characters. In other words, the natural system is that ar- 
rangement in which the distance from each species to every 
other is in exact proportion to the degree in which the essential 
characters of the respective species agree. Hence it follows that 
the whole difficulty of discovering the natural system consists 
in forming a right estimate of these degrees of resemblance. 
For the degree in which one species resembles another must 
not be estimated merely by the conspicuousness or numerical 
amount of the points of agreement, but also by the physiolo- 
gical importance of these characters to the existence of the spe- 
cies. On this point no certain rules have yet been laid down ; 
for though naturalists in general admit, for instance, that the 
* Read before the Zoological Section at Glasgow, Sept. 21, 1840, 
