6i2 THE POPULAR SCIENCE MONTHLY. 



compsognathus and his cousin the archseopteryx. One of these first 

 sketches, the ichthyornis, has a row of teeth in each jaw, and displays 

 another strikingly early reptilian or fish-like peculiarity in the joints 

 of its backbone, which are cup-shaped or hollow on either side, exactly 

 like those of a cod. This strange bird must have resembled an emu in 

 many respects, and it might easily have devoured the large ganoid fish 

 of this period with its formidable jaws. Still more reptilian in some 

 particulars is the hesperornis, also found in the Western American 

 chalk. Hesperornis was a huge swimming ostrich, and it had pointed 

 teeth like a crocodile's, set in a groove running down the jawbone. 

 They were supported on stout fangs, in the same way as the teeth of its 

 reptilian allies, the mosasaurians. Like the ostrich, hesperornis had a 

 broad breast-bone, but this breast-bone was destitute of a keel, as is 

 still the case in all the ostrich family. The wings were also very im- 

 perfect, like those of the cassowaries. In its tail, hesperornis resem- 

 bled its predecessor, archseopteryx, so far as regards the lizard-like 

 separateness of the vertebrae, except at the extreme end, where they 

 were slightly massed together into the first resemblance of a plowshare- 

 bone, such as the one I hold in my hand. Thus these two interme- 

 diate birds of the chalk period, though slightly more bird-like than 

 their cousins of the oolitic age, still retained, each in its own way, 

 many unmistakable relics of their descent from reptilian or almost 

 amphibian ancestors. As usual, the further back we go, the more do 

 we find all the lines converging toward a common center. 



The primitive teeth died slowly and gradually out as time went on. 

 In the still later eocene deposits of the London clay in the Isle of 

 Sheppey, we find the remains of a true bird, known as odontopteryx, 

 in which the teeth have entirely coalesced with the beak, and have 

 assumed the form of bony projections. Strict biologists will tell us 

 that these projections are not teeth at all, because true teeth are not 

 bony in structure, and are developed from the skin of the gums. But 

 such hair-splitting distinctions are of little value from the evolutionary 

 point of view ; the really important fact to observe is this, that while 

 hesperornis has teeth in a groove, reptile-fashion, ichthyornis has 

 teeth in distinct sockets, mammal-fashion, and odontopteryx has them 

 reduced to bony projections from the bill, in a fashion all its own, thus 

 leading the way to modern birds, in which the teeth are wholly want- 

 ing and the bill alone remains. Indeed, among our existing kinds 

 there are some which still keep up some dim memory of the odonto- 

 pteryx stage ; for the merganser, a swimming fish-eating bird, has bony 

 ridges on its bill, which help it to grasp its prey ; and the South 

 American leaf -cutter has a double set of bony bosses on its beak and 

 palate. 



The most apparently distinctive feature of birds lies in the fact 

 that they fly. It is this that gives them their feathers, their wings, 

 and their peculiar bony structure. And yet, truism as such a state- 



