50 EXTINCT MONSTERS. 
although not couched in the language used by men of science—to 
give a fair idea of its structure and habits. 
In conclusion, a few words may be said about the ancestry and 
life-history of these ancient monsters. Palontologists have good 
reason to believe that they were descended from some early form 
of land reptile. Ifso, they show that whales are not the first land 
animals that have gone back to the sea, from which so many 
forms of life have taken their rise. 
During the long Mesozoic period fish-lizards played the part 
that whales now play in the economy of the world; and they 
resembled the latter, not only in general shape, but in the situation 
of the nostrils (near the eye), and in their teeth and long jaws. 
But these curious resemblances must not be interpreted to mean 
that whales and fish-lizards are related to each other. They only 
show that similar modes of life tend to produce artificial re- 
semblances—just as some whales, in their turn, show a superficial 
resemblance to fishes. 
With regard to the particular form of me from which the 
fish-lizard may have been derived, no certain conclusion has at 
present been arrived at. ‘This is chiefly from want of fuller 
knowledge of early forms, such as may have existed in the previous 
periods known as the Carboniferous and Trias (see Appendix I.). 
But there are certain features in the skulls, teeth, and vertebree 
that suggest a relationship with the Labyrinthodonts, or primeval 
salamanders that flourished during the above periods, or at least 
from amphibians more or less closely allied to them. They can- 
not by any possibility be regarded as modified fishes ; for fishes 
have gills instead of lungs. 
The fish-lizards played their part, and played it admirably ; but 
their days were numbered, and the place they occupied has since 
been taken by a higher type—the mammal. As reptiles, they 
were eminently a success; but, then, they were only reptiles, and 
therefore were at last left behind in the struggle for existence, 
until finally they died out, at the end of the Cretaceous period, 
