SYSTEM OF NATURE. 
117 
confusing the results of their combination, has arisen the 
hypothesis known as the theory of affinities and analogies. 
Not only are these terms objectionable as conveying to the 
mind no definite idea, but, as they are employed by natu¬ 
ralists, they are wholly devoid of fixed meaning, because 
capable of bearing any meaning : it having always been 
regarded as optional with a systematist, whether he should 
consider any given resemblance a relation of affinity or one 
of analogy. The System of Nature has but two sources 
of character, — structure and economy ; these are definite; 
and it need scarcely be asserted that the former is ever 
modified in accordance with the requirings of the latter. 
Let us commence our examination of the radii with the 
one which I have termed aerial. Tracing the course of 
each radius through a series of circles, whose contents 
have already been detailed and their relative positions laid 
down, necessarily involves considerable repetition, but such 
repetition appears preferable to the obscurity attendant on 
a too hasty dismissal of this branch of the enquiry. I 
need scarcely remind my readers, that as three out of every 
six groups are supposed to recede from the centre farther 
than the other three, and consequently occupy places in 
another circle, a direct line drawn from the circumference 
to the centre can only intersect groups situate in alternate 
rings: thus the aerial radius passes through four groups 
instead of eight; these are the province Pterota, the class 
Aves, the tribe Cheiroptera and the order or family Galeo- 
pithecidae.* It will at once be seen that the radius in 
question, as it intersects each of these groups, commu- 
* I find all our most able zoologists insist on placing the Hying le¬ 
mur (Galeopitliecus) among tlie Primates; and I avail myself of this 
opinion in preference to my own adopted from Cuvier. 
