Bees aig Fs aes See Ser COTES Pky Nee ee n 
1884. ] Growth, its Conditions and Variations. 1211 
the vertebrate. The Paleozoic fishes appeared. At first they 
must have been inferior in size, weapons and food-getting power 
to their invertebrate rivals, who so long had ruled the sea. But 
their superiority of organization quickly told. They came into 
competition with their former superiors, and soon progressed be- 
yond them, gaining massive armor of defence and strong reptilian 
teeth for attack. The empire of the seas had passed into new 
hands. These great ganoid and dipnoid fishes increased in size 
and strength, the invertebrate wave sank before them, and the 
lordship of the ocean became their own. The result was the 
same that has appeared in all such cases. They not only grew 
great in bulk, from the abundance of their food supply, but they 
varied with the greatest rapidity in specific character, assuming 
every variety of adaptation to their variety of food. This rapid 
Specific variation of each type of life immediately after gaining 
the supremacy over preceding dominant types, is a fact which 
May be traced throughout the geological age, and indicates that 
Variation in form and habits, while slow under ordinary condi- 
tions, may be extremely rapid under such specially favoring cir- 
cumstances. 
These early dominant fish, while superior in power to all pre- 
ceding animals, were inferior to those that succeeded them in the 
fact that they trusted for defence to massive armor instead of to 
speed. In the whole history of life trust to armor has been an 
inferior characteristic, the armored animals have tended to grow 
More sluggish, and in most cases to assume a sedentary life, 
While all steps of higher development have been attained by the 
weighted and swifter moving animals. Such is the story of 
ocean life. As we enter the Mesozoic age unarmored reptiles 
Succeed to the armored ganoids and quickly take from them the 
“mpire of the seas. The duplex characteristics of the Palzozoic 
fishes seem to divide, developing in one direction into the more 
efficient reptiles, and in the other into the teleostean fishes, which 
ae well adapted to obtain food from the humbler life of the sea. 
`œ only continuous representative of the eatlier dominant fishes 
S the shark, which had cast off its excess weight and a ap 
“me able to contest the field with the swimming reptiles, and 
"Yen to survive them. But the immense size attained by these 
ie.. - mp 
ag details of this hypothesis see paper by Alpheus Hyatt, Science. 5 
