that the water was unfit for the ordinary fishes. Thus, though at first sight the possession of external armour and means to respire air, in the case of these peculiar fishes, may seem to have no direct connection with each other, their obvious correlation in some modern ganoids may have had its parallel on a more extensive scale among their ancient relatives. Just as the modern gar-fish, by virtue of its lungs, can live in stagnant shallows and hunt frogs, but on that account needs strong armour to defend it against the foes that assail it in such places; so in the Devonian the capacity to inhabit unaërated water and defensive plates and scales may have been alike necessary, especially to the feebler tribes of fishes. We shall find that in the succeeding carboniferous period there is equally good evidence of this. We have reserved little space for the Devonian plants and insects; but we may notice both in a walk through a Devonian forest, in which we may include the vegetation of the several subordinate periods into which this great era was divisible. The Devonian woods were probably, like those of the succeeding carboniferous period, dense and dark, composed of but few species of plants, and these somewhat monotonous in appearance, and spreading out into broad swampy jungles, encroaching on the shallow bays and estuaries. Landing on one of these flats, we may first cast our eyes over a wide expanse, covered with what at a distance we might regard as reeds or rushes. But on a near approach they appear very different; rising in slender, graceful stems, they fork again and again, and their thin branches are sparsely covered with minute needle-like leaves, while the young shoots curl over in graceful tresses, and the older are covered with little oval fruits, or spore-cases; for these plants are cryptogamous, or flowerless. This singular vegetation stretches for miles along the muddy flats, and rises to a height of two or three feet from a knotted mass of cylindrical roots or root-stocks, twining like snakes through and over the soil. This plant may, according as we are influenced by its fruit or structure, be regarded as allied to the modern club-mosses or the modern pill-worts. It is _Psilophyton_, in every country one of the most characteristic plants of the period, though, when imperfectly preserved, often relegated by careless and unskilled observers to the all-engulfing group of fucoids. A little further inland we see a grove of graceful trees, forking like _Psilophyton_, but of grander dimensions, and with the branches covered with linear leaves, and sometimes terminated by cones. These are _Lepidodendra_, gigantic club-mosses, which were developed to still greater dimensions in the coal period. Near these we may see a still more curious tree, more erect in its growth, with rounded and somewhat rigid leaves and cones of different form, and with huge cable-like roots, penetrating the mud, and pitted with the marks of long rootlets.