M. Albert Gaudry, in a review of the course of development of animate nature through the geological ages, remarks on a curious analogy between the changes experienced by fishes in the Secondary age and those which modern warships are passing through. As soon as the thought of armoring vessels took effect, stronger projectiles were devised, in order to penetrate the armor. Then the armor had to be strengthened, and just as rapidly as the plates were made thicker, more enormous projectiles were cast; so that the race has culminated in the construction of vessels so heavy that they are almost unmanageable, and thought is turning again toward light, swift boats. With the Secondary fishes, too, offensive arms and defensive armor were developed pace by pace. The teeth were modified till they could crush through the hard cuirasses of the ganoids, and the Secondary beds are characterized by marine animals thus furnished. Powerful grinding teeth are found in the bony and the cartilaginous fishes, and even in many of the massive reptiles of the Trias. The fishes, exposed to enemies whose instruments of offense matched their defensive armor, were obliged to seek safety in flight. Their vertebral column became more solid, so as to furnish a strong support to their spinal muscles, and their tails were shortened and broadened so as to become instruments of energetic locomotion. When this transformation was completed, the carnivorous fishes had no more use for crushing teeth, and they have almost disappeared; no more marine reptiles with teeth like paving stones are found in the Tertiary beds or in modern times; and fishes with large teeth working like millstones are rare in comparison to those which have thin cutting teeth; and power resides in agility to reach the goal or escape the danger. Existing fishes are marked by an activity that was unknown in the ancient oceans, and justify the observation of Moquen Tandon. that "the agitation and inconstancy of the sea seem to have impressed themselves on the beings which live in its waves, in the suppleness, rapidity, and vivacity of their movements."