16 
end; or, in other words, that final causes do not explain all the afti- 
nities and resemblances which we are able to trace*. 
And again, it must be observed, that those remarkable likenesses, 
which are observable in many or all animals, between their various 
forms and conditions up to maturity, on the one side, and the various 
members of the animal kingdom up to their own position in the 
scale, on the other hand (so that, for instance, man passes through 
forms resembling, but not identical with, those of many animals from 
the lowest monad up to his own position in the scale), are inexpli- 
cable on the theory that the forms of animals are regulated by final 
causes only; but are in perfect accordance with that other which 
holds that there is expressed in the structure of animals some abstract 
idea, which running through all the frame, and modified to all pur- 
poses of need, and manifested in all variety of conditions, is yet one 
and the same. 
It must be admitted that the force of these arguments may, to 
some extent, be barred by an assertion which it is difficult fully to 
answer, viz. that our ignorance of final causes is so great as to allow 
us no room to argue on the existence of other causes from their ap- 
parent inadequacy ; nevertheless as the other supposition seems to 
have in it no improbability, but as I think the contrary, it may be 
admitted as at least what best suits our present knowledge. 
The belief in the existence of other laws of organization besides 
that of final causes does in no wise lessen or obscure the argument of 
natural religion derived from it, which was advanced with great per- 
tinency by the ancient Stoical philosophers, and has been amplified 
by Derham, Paley and others in our own country. 
I now proceed to the second portion of my paper. 
Srection II. 
There are reasons derived from the structure of animals below 
the Vertebrata which might induce us to expect that the vertebrate 
skeleton should be composed of elements of a common character. 
1. So soon as the nervous system assumes the form of a line or 
chain down the body of the animal, the whole structure puts on a 
segmental or annular arrangement. Thus in the Annelida the body 
consists of numerous segments, similar one to the other, with the 
exception of the anterior one or head, which is sometimes slightly. 
different in form, but in other instances only distinguishable by the 
presence of a mouth. Each segment has its proper nervous ganglion, 
connected by two fibrous commissures with those of the neighbouring 
division. 
2. But these segments are subject to change. Thus the Poly- 
desmide, a family of the Myriapoda, exhibit the posterior part of 
the body composed of segments similar to those above described, 
whilst in the anterior part each segment is the result of the coales- 
cence of two original ones. In the Chilipoda, the same process has 
* This part of the subject has been fully illustrated by Prof. Owen in his 
various writings. 
