PRESIDENT’S ADDRESS. 353 
attaining their maximum in the Silurian period, and becoming 
extinct before the end of the Palzeozoic era. 
Of plants we have at last certain knowledge. The first un- 
doubted seaweed (Buthotrephis) occurs in Lower Ordovician rocks, 
while from the Silurian there are many beautifully preserved 
forms ; from which we may infer that the Cambrian, and most of 
the Ordovician, seaweeds were too delicate in structure to be pre- 
served. But in addition to seaweeds there were also land plants. 
In the Upper Ordovician, the extraordinary tree-like Protoaxites 
seems to have been a terrestrial Alga, while Protostigma is related 
to Sigillaria, and itis to Protostigma that the prickly macrospores 
from Bohemia, discovered by Dr. Riist, probably belong. In the 
Silurian period there were two genera of Lycopodiacece (Pstlophytum 
and Glyptodendron), and at least two genera of LHquisetacece 
(Annularia and Sphenophyllum). \ Ferns, apparently, were not 
yet in existence, for the so-called Hopteris is now known to be 
nothing more than a growth of dendritic crystals. 
Land Animals.—Rather above the horizon on which the first 
Jand-plants occur—that is, in the Silurian—the oldest known insect, 
Paleoblattina douwvillei, has been found in France ; and, although 
its affinities are rather uncertain, it is thought by Brongniart to 
belong to the Orthoptera. In the Devonian, neuropterous insects 
(May-flies) came on the scene ; and in the Carboniferous there were 
many Orthoptera, Neuroptera, and, perhaps, Hemiptera. No other 
order of insects appear at that time to have been in existence. 
Scorpions, with stings at the end of their tails, like those of the 
present day, and, therefore, carnivorous, have been found in the 
Silurian, and spiders in the Carboniferous. The fact that carni- 
vorous scorpions have been found as low down as the oldest- known 
phytophagous insect, is good evidence that insects must have 
existed on the land for some time previously ; so that we may with 
some confidence refer their origin to the Ordovician period. 
SPECULATIONS ON ORDOVICIAN AND SILURIAN LIFE. 
The peopling of the shore-line and the land.—Probably all the 
different sub-kingdoms of animals had come into existence before: 
the close of the Cambrian period. Henceforward no more funda- 
mental types were to be introduced ; multiplication and variation 
of the existing types was for the future to be the réle, until all 
habitable parts of the earth were filled with life. It is in the early 
part of the Ordovician period that we first see animals fitted to 
live in the rough waters of the littoral zone of the sea-shore : these 
were thick-shelled gastropods, followed in the Upper Ordovician by 
the Ostracoderma. And it is in the Upper Ordovician that we have 
the first proofs of the existence of land-plants, followed in the 
Silurian by insects feeding on plants, and scorpions feeding on 
insects, 
Z 
