Marvels of the Universe 895 
answering to the fore-limbs have changed less than the hind-legs, which have become excessively 
shortened, and incapable of being flexed, as are the hind-legs of terrestrial animals. In the whales 
this transformation has proceeded yet further. Herein the fore-limbs have become so changed as 
to be totally unlike those of land-dwellers. No fingers are visible, and when the hand is dissected 
these fingers are found tightly bound together and enormously lengthened. The hind-legs have 
vanished completely. In the old fish-lizards, and in the penguins, among birds, we find the fore- 
limbs changed in response to this aquatic life. But the change has not been effected to attain quite 
the same ends; for in the fish-lizards and whales the paddles serve simply as balancers ; in the 
penguins they are propellers, for the penguin swims by means of its paddles, which are modified 
wings, which its ancestors used to fly with. This being so, it is curious that the hippo- 
potamus, one of the most aquatic of mammals, displays not the slightest evidence of this fact in 
the shape of its legs. 
Now what is true of aquatic is true also of land animals, though the causes, or stimuli, to the 
changes are often difficult of discernment. What, for example, determined the evolution of the 
snakes 2? These creatures, we know, once possessed limbs like those of the lizard ; and evidence of 
this fact is to be found in vestiges of the hind-limbs, which, in the pythons, for instance, are to be 
found at the base of the tail. And this loss of the limbs, it is to be noted, has gone hand in hand 
with a lengthening of the body, the number of the vertebree which make up the backbone having 
been enormously increased. More on this head of the evolution of the snake we cannot say ; the 
theme has been introduced because of its important bearing on what follows. 
Briefly, there are certain lizards which, superficially, are so like snakes that only an expert 
can tell the one from the other. Our common Slow-worm is one of these. Every trace of 
Photo by] [W. B. Johnson. 
THE SLOW-WORM. 
Another degenerate from the Lizard type. In some specimens of the Slow-worm signs of rudimentary legs may be dis- 
tinguished, but in others external marks have completely disappeared. It should be noted that the folk-name of this animal is 
entirely a misnomer, for it is no worm, but a true Lizard. 
