1212 Growth, its Conditions and Variations. [December, 
reptiles, and their rapid variation in specific character, indicate 
their superiority over all the remaining ocean life of their period, 
the abundant food which they obtained with little effort, and the 
variety in organization and methods of escape of this food, which 
necessitated accordant variations in its foes. 
While these revolutions were taking place in the empire of the 
seas, life had invaded the land. Insects were the first animal in- 
habitants of the land, so far as evidence goes. They gained no 
extreme size, perhaps through a paucity of food supply and 
organic inefficiency. Yet land articulates seem to have rapidly 
increased in variety, since Spiders, scorpions and myriapods 
appear almost contemporaneously with insects. At the same 
period, or shortly afterwards, ocean vertebrates invaded the 
land. The character of their invasion singularly resembles that 
of the articulates. The latter were obviously derived from water 
articulates, since the first known forms belong to those families 
which pass their larval period in the water. In like manner the 
earliest land vertebrates were batrachians, which in their larval 
State are water animals. These creatures seem to have founda 
free field and abundant food, and to have multiplied and varied 
with great rapidity, while some of them attained great bulk 
despite their imperfect organization. Cope gives a list of thirty- 
nine genera and about a hundred species of Carboniferous batrach- 
ians, which indicates that the full degree of specific variation was 
very great. In fact they seem to have had the world of the land 
to themselves, with nothing but the imperfection of their organ a 
zation to hinder their obtaining superabundant food with little 
exertion, and thus growing to immense size. 5 
This age of batrachian dominance was succeeded by one 
which the wave of batrachian life declined, while huge land ani- 
mals took their place on the throne of the empire of life. The 
batrachians were unfitted to compete with reptiles in the struggle 
for food, and were obliged to content themselves with lesser nf 
plies, so that they quickly diminished in size before the poste 
their strong competitors. Very probably personal assault is 
these new-comers, as they grew stronger and able to cope Nae 
the batrachians, hastened the decline of the latter, and dro 
them down into the humbler fields of life. : i 
And now came a new life era. The land reptiles increased 
number and variety with the seeming suddenness of all p 
