EVOLUTION OF LIFE. 
114 
fish were the oldest of the Echinodermata, the Brachiopoda 
of Mollusca, the Entomostraca of Crustacea, and that the 
Worms preceded the Insects, etc. We have just seen that 
the life of the Silurian, the most ancient period except the 
Azoic, was characterized by these very orders, which are 
the most simply organized of the respective divisions of 
the animal kingdom, while the Fucoida, or brown sea- 
weed, found fossil in rocks of this period, belong to the 
Alge, the simplest division of the vegetal kingdom. 
Geological evidence confirms, therefore, not only in a 
general way, but to an extent in detail not to be hoped for 
from the nature of the subject, the view of the development 
of the animal and vegetal kingdoms deduced from their 
structure. The Silurian period is sometimes called the 
Age of Mollusca and Algae. 
AGE OF FISHES. 
Passing from the Silurian period to the Devonian, so 
called from the rocks of this formation having been fist 
studied in Devonshire, England, we notice that while the 
first half of the Devonian agrees in its main features with 
the latter half of the Silurian, the latter half of the Devo- 
nian, often called the Old Red Sandstone, offers evidence of 
a progress in life, since its rocks contain the remains* of 
fish, together with a few Ferns, Lycopods, and Conifers. The 
remains of these plants are, however, only rarely found in 
the Devonian; the flora of this period, as well as that of the 
Silurian, being more generally characterized by the presence 
of Alge. The Fishes found in the Devonian period are 
Sharks and Ganoids (Fig. 147) The Sharks belong to 
the order of Cestraphori, or weapon-bearers, so named from 
their dorsal fin being armed with a long spine; these spines 
* Fish-remains found in the Silurian of England. 
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