666 Marvels of the Universe 
can be bent this way and that. 
In like manner the ribs are, or 
should be, ‘“‘ well covered.’ So 
it was in times past with the for- 
bears of the Tortoise. But in 
them the skin was provided with 
an armature of bony knobs, to 
serve, perchance, as a coat of 
mail to withstand the blows of 
enemies. In course of time this 
armature grew more seeming per- 
fect. The separate “ bosses”’ of 
bone became welded to form a 
shield: hard and inflexible : a very 
efficient protection, no doubt, yet 
one for which a heavy penalty was 
to be exacted from the Tortoise 
yet unborn! For as the shield 
increased in perfection so _ it 
limited the movements of the 
back ; and so, in proportion, the 
THEN SHEL OFNA CLORTOISE: muscles of the back degenerated, 
Here the skeleton on a Leathery Turtle is shown with the horny covering  $YOWing less and less in volume in 
(PRb eho it for a shell) lifted up to show how entirely separate it is each generation. As the muscles 
shrank, so the shield descended, till 
at last it rested on the spines which project from the backbone, leaving but a small space between 
the shield and the ribs. Then the spines became reduced in length from lack of use as supports 
for muscle, and the shield sank lower still, till it rested on the ribs themselves. Then, last stage of 
all, the ribs and the shield merged, the one into the other, until to-day the ribs themselves have 
vanished, leaving only their heads and their lower ends, which may readily be made out in a dried 
skeleton of any Tortoise or Turtle. While of the backbone little more than a tube remains for 
the passage of the spinal cord. 
Now is this capable of proof ? I hear someone ask. Of reasonable proof—yes. And the evidence 
may be obtained from certain marine Tortoises commonly known as Turtles. In the species known 
as the Leathery Turtle, or “ Huth,” the shield is made up of innumerable little discs of bone closely 
interlocked by means of toothed edges to form a kind of mosaic, and over this is stretched, as it 
were, a leathery skin. When this shield is raised there will be found underneath a thin layer of 
muscle or “ flesh,” covering the backbone and ribs ; and when the skeleton is examined these ribs, 
and the backbone itself, will be found to have preserved their integrity. The accompanying photo- 
graph should make this much clear. Now when we turn to the examination of any other member 
of the Tortoise-tribe—be it Tortoise or Turtle—we shall find a very different state of things. The 
shield can no longér be raised without exposing the whole of the internal organs of the body ; and 
when we come to inquire as to the reason of this, we find that the shield and the ribs have come to 
fuse into one common mass of bone, the only means of identifying the ribs being, as we have said, 
by the traces of their lower ends and of the “‘ heads,” whereby in times past they were jointed on 
to the backbone. That this is so is no mere guess-work, for every Tortoise, in the course of its 
growth from the egg to the adult, passes through the ancestral stages. So that if we select the right 
period of growth for our examination we shall find a stage answering to that seen in the adult 
Leathery Turtle ; that is to say, a stage displaying complete ribs distinct from the outer shell. 
