WATER TO LAND

Evening Post, Volume CXVI, Issue 104, 30 October 1933, Page 6

WATER TO LAND

SCIENTIST'S TALK

ORIGIN OF VERTEBRATES

COMMON ANCESTORS

(From "The Post's" Representative.) LONDON, September 13. Professor Watson, F.E.S., of University College, London, gave an interesting discourse <tm "The Origin of Land Vertebrates" at the British Association Conference. Ho traced tho origin back to the Devonian and Silurian geological epochs, when, as was clear from the ovidenco of the rocks, there were conditions of great aridity with alternating flooding and drying •of streams and lakes. Tho ancestors of tho cartilaginous fishes remained in the sea, and had no occasion to change their modo of obtaining oxygen.

Tho three groups of bony fish now represented by the lung-fish, the ordinary bony fish, and tho Polypterus-like fish wore all inhabitants of fresh water, and when the streams became stagnant and began to dry up they had to resort to air breathing. There was abundant evidence that the swim-bladder which most modern fish possessed was originally an air-breathing organ, and was tho origin of the lungs of all airbroathing animals. In many modern fish it had lost this primitive function, and had become a hydrostatic organ to enable the fish, which was heavier than water, to keop afloat or to ascend from depths whore the pressure was greater, a function which it carried out by secreting oxygen from tho blood into the air-bladder in exact proportion to tho pressure of the water at different depths. ' ' . . LUNG-FISHES. Speaking of the modern lung-fishes, he said the Ceratodus, the Australian lung-fish, lived only in two river systems in Queensland. These rivers never completely dried up, there being large pools many feet deep, os en in the driest season. Tho eggs were laid singly and the tadpoles when hatched had no need of a special breathing apparatus. They were the most ancient arid most primitive of the group.; The American lung-fish, Lcpidosiren, and the 'African, lung-fish, Protopterus, on) the other hand, lived in ■ huge tropical swamps. As these dried up,\ the water became foul ■ with 1 dead animals and decaying plants, and had been proved by Dr. Carter to contain no oxygen in solution. When the water began to disappear altogether these; fishes enclosed themselves in cocoons of mud and mucus, which they, excreted, and it was in these cocoons that they were transported to Europe and released by dissolv- j ing tho dry mud in warm water. Their, larvae, as a breathing device when they were hatched in water containing little oxygen in solution, developed external j gills, filaments of a definite structurel reproduced exactly in those amphibians j which permanently retained their tails,', but never found in the frogs and toads. ANCESTORS OF MAMMALS. Professor Watson described the ancestral types of fish which were the common ancestors of mammals, reptiles, and amphibians, and showed how repeatedly a typo of head, cylindrical in section, with a single cardyle and very thick base, had been flattened, its base] thinned and the single cardyle replaced by two in accordance with the habits of | tbo animals. Ho said that probably all the amphibians had originally beeuj purely acquatic, and; had used the j primitive air-bladder as an accessory- to tlieiv truo, gills, but' that some had. bo-1 eonio terrestrial, changing: their strue-j turc in accordance with their new j environment. Of these, some, like the gigantic labyrinthodonts, had ultimately perished; some like tho frogs and toads had remained amphibians, and others like the urodeles had returned secondarily to the water, some of thorn dropping out the land stage altogether. The external gills, which had been thought an ancestral character, were undoubtedly comparatively late "adaptations, and wore instances not of autogeny repeating phylogeny, but of true larval organs being carried over into adult life.

the-New Zealanders a rich chance of winning this game. Had they attacked Quist they would . probably have taken the game with the chance of a 54 lead. As it was, Quist saved, the game and Malfrpy lost his next service to love, on three errors and a double-fault, anfl the set score-was evened. In the final'set neither /New Zealander was playing.well enough to halt the Australians' progress. '■/■:V The final double of the day, between Turnbull arid 'Quist and Lee and Wilde, had not been long under way when rain compelled the abandonment of play.