The Outline of History: Being a Plain History of Life and Mankind

ater. § 2. The

that life went on in and by and with water as it

ad no protection. But in a world of rain-pools and shallow seas and tides, any variation that enabled a living thing to hold out and keep its moisture during hours of low tide of drought met with every encouragement in the circumst

But a creature that is to be exposed for any time out of the water, must have its body and its breathing apparatus protected from drying up. Before the seaweeds could creep up out of the Early Pal?ozoic seas into the intertidal line of the beach, they had to develop a tougher outer skin to hold their moisture. Before the ancestor of the sea scorpion could survive being left by the tide it had to develop its casing and armour. The trilobites probably developed their tough cove

er, were distributed by water and could only germinate under water. The early plants were tied, and most lowly plants to-day are tied, by the conditions of their life cycle, to water. But here again there was a great advantage to be got by the development of some protection of the spores from drought that would enable reproduction to occur without submergence. So soon as a species could do that, it could live and reproduce and spread above the high-water mark, bathed in light and out of reach of the beating and distress of the waves. The main classificatory divisions of the larger pla

Age by nature's method of experiment and trial. Then slowly, but in great abundance, a variety of new plants began t

plants came th

tubes, the tracheal tubes, which carry the air all over the body before it is dissolved. In the case of the vertebrated land animals, the gills of the ancestral fish were first supplemented and then replaced by a bag-like growth from the throat, the primitive lung swimming-bladder. To this day there survive certain mudfish which enable us to understand very clearly the method by which the vertebrated land animals worked their way out of the water. These creatures (e.g. the African lung fish) are found in tropical regions in which there is a rainy full season and a dry season, during which the rivers become mere ditches of baked mud. During the rainy season these fish sw

ter; then a gill cover grows back over them and forms a gill chamber. Then, as the creature's legs appear and its tail is absorbed, it begins to use its lungs, and its gills dwindle and vanish. The adult frog can live all the rest of its days in the air, but it can be drowned if it is kept steadfastly below water. When

Lung fish b

e land. Geographically, all round the northern half of the world it was an age of lagoons and shallow seas very favourable to this invasio

of the Late

he form of huge-stemmed trees, of which great multitudes of trunks survive fossilized to this day. Some of these trees were over a hundred feet high, of orders and classes now vanished from the world. They stood with their stems in the water

Belgian coal-measures had a wing span of twenty-nine inches! There were also a great variety of flying cockroaches. Scorpions abounded, and a number of early spiders, which, however, had no spinnerets for web making.[12] Land snails appeared. So too did t

s at all; wallowing amphibia and primitive reptiles were the very highest creatures that life had so far produced. Whatever land lay away from the water or high abo