132 
THE GEOLOGIST. 
as proof has been adduced, of the development of one good natural 
species into another ; but there is evidence of a development of plan, 
and that de\'elopment is but revealed to us in the occurrence, in these 
ancient life-periods, in succession of similar or kindred forms. Ever 
as the circumstances of their life are becoming alike, the species ne- 
cessarily approach and resemble. 
The history of Acanthodes, thus brought before us, almost warrants 
these conclusions: — First, there are no gaps, either in the succession 
of strata or in the course of creation, at least over lengthened periods, 
embracing it may be several so-called geological systems. A narrow 
horizon may indeed give the idea of wreck, but when the horizon of 
our observation is broadened, the chasms disappear. Secondly, there 
is evidence, at least in Acanthodes, there is no symptom of one true 
and good natural species developing into another, particularly not 
into a higher or advanced form. Thirdly, nor is there, as has been 
contended for by some writers, a degradation, either in size or in 
beauty, and other features of form, among species of the same genus, 
whose existence stretches over a long period. Fourthly. "What how- 
ever may be called digression or even retrogression of form appears in 
the development of the scheme of an Organized Creation. There is 
digression or departure from the type to put on some specific cha- 
racter towards an adaptation to some new circumstance in the life of 
the species ; and again there is retrogression, a throwing off again of 
the specific or induced characteristic, and a return to the primitive 
or naked type. The mould in which the life is cast is not broken, 
but enlarged ; yet after being enlarged, it is often again contracted 
ere the genus disappears in the onward current of the ages. 
It is matter of regret with us now that when Egerton described in 
the decade of the Geological Survey the species of Acanthodes from 
the Lower Devonian, all our materials were not put into his hands. 
Distance is a sufficient excuse, but it is necessary to supplement his 
description by one or two remarks. The species occurs of a very 
small size. We have a specimen, scarce half an inch in length, a very 
minim of creation, but a perfect portrait in itself, with its every spine 
and every scale in their place. When well preserved, the scale ap- 
pears to be perfectly smooth, and not ornamented in the least. And 
in many specimens there is a display of several small spines between 
the pectorals and the ventrals, as if the creature had an undercrop 
of rudimentary fins, which were attached to the spines, for the pro- 
pulsion of its graceful and slim figure through the waters, and for its 
escape from its many enemies. The species occurs in our Old lied 
beds over almost the whole county of Forfar, and in the neighbour- 
ing county of Kincardine, and should be looked for in the equivalent 
beds of England. 
