IN his third talk, Professor Swinnerton will tell one of the greatest chapters in the story of life: how the amphibious creatures first crept on to the solid earth, how they developed into the reptiles which dominated the globe throughout an age, to give place in turn to the mammals that constitute the highest development of life that we know. And side by side with the main line of evolution are the branch lines that sprang forth and died out, Jeavfng the sole record of their existence written in the rocks.