Salt water covers seventy per cent of the earth's surface; a gigantic challenge to our curiosity and scientific skill.

Marine biologists are slowly unravelling the complex and inter-related life cycles of the animals in the sea.
Peter Stone introduces the last of four programmes.
With Dr. D. H. Cushing and Dr. F. R. Harden Jones, Fisheries Laboratory, Lowestoft.
(First shown on BBC-2)

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