Origin of Species Variorum

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 seems hopeless: who will decide whether a cuttlefish 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, for instance, not very high in their own class, might beat the cephalopods or highest molluscs; and such crustaceans, though not highly developed, would stand very high in the scale of invertebrate animals 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 distant 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 molluscs, namely, cephalopods and brachiopods, swarmed in numbers: at the present time both these orders have been greatly reduced, whereas other orders, intermediate in grade of organisation, have largely increased; consequently some naturalists have maintained that molluscs were formerly more highly developed than at present; but a stronger case can be made out on the other side, by considering the vast reduction at the present day of the lowest molluscs, more especially as the existing cephalopods, though so few in number, are more highly organised than their ancient representatives. We ought also to