The recent spread of the free-diving technique has made direct contact with the sublittoral environment relatively simple. The advantages of this to the ecologist need not be stressed.

The rather more cumbersome and expensive standard diving method had had already been used by Gislén (1930), Kitching, Macan & Gilson (1934), Kitching (1937, 1941), Zalokar (1942), Bursa, Wojtusiak & Wojtusiak (1948) and Waern (1952). Drach (1948 a,b, 1949, 1951) was the first to exploit free diving for ecological purposes and was followed by Forster (1954, 1955, 1958), Pérès & Piccard (1949), Ernst (1955), Laborel & Vacelet (1958), Knight-Jones & Clifford Jones (1956) and Aleem (1956).