180 
THE GEOLOGICAL MIDDLE AGE. 
mesticated animals and cultivated plants, which 
can never be made a test of the origin of wild 
species.* 
In my next article I shall show the relation be- 
tween the Cretaceous and Tertiary epochs, and 
see whether there is any reason to believe that 
the gigantic Mammalia of more modern times 
were derived from the Reptiles of the Secondary 
age. 
* The advocates of the development-theory allude to the meta- 
morphosis of animals and plants as supporting their view of a 
change of one species into another. They compare the passage 
of a common leaf into the calyx or crown-leaves in plants, or 
that of a larva into a perfect insect, to the passage of one spe- 
cies into another. The only objection to this argument seems 
to be, that, whereas Nature daily presents us myriads of ex- 
amples of the one set of phenomena, showing it to be a norm, 
not a single instance of the other has ever been known to occur 
either in the animal or in the vegetable kingdom. 
