To attempt to compare members of distinct types in the scale of highness 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, not very high in their own class, might beat cephalopods, the 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. Beside 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 two periods.