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between the selaceans and teleosteans; the latter at the present day are largely preponderant in number; but formerly selaceans and ganoids alone existed; and in this case, according to the standard of highness chosen, so will it be said that fishes have advanced or retrograded in organisation. To attempt to compare
→in the scale of highness members of distinct types
who will decide whether a
be higher than a bee— that insect which the great Von Baer believed to be "in fact more highly organised than a fish, although upon another type"? In the complex struggle for life it is quite credible that crustaceans,
not very high in their own class, might beat
highest
and such crustaceans, though not highly developed, would stand very high in the scale of invertebrate
if judged by the most decisive of all trials— the law of battle. Besides these inherent difficulties in deciding which forms are the most advanced in organisation, we ought not solely to compare the highest members of a class at any two
periods— though undoubtedly this is one and perhaps the most important element in striking a balance— but we ought to compare all the members, high and low, at the two periods. At an ancient epoch the highest and lowest
namely, cephalopods and brachiopods, swarmed in
at the present time both
→orders are
greatly reduced,
intermediate in
organisation, have
increased; consequently some naturalists
that
were formerly more highly developed than at present; but a stronger case can be made out on the
side, by considering the vast reduction
→of the lowest molluscs, and the fact that our
existing cephalopods, though
few in number, are more highly organised than their ancient representatives. We ought also to
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