“…Later, Rothschild (1949), Borei (1951) and Yeas (1954), using the method of Keilin andHartree (1939, 1949) of intensifying cytochrome bands by cooling the material in liquid air. were able to demonstrate the bands of cytochromes a and h. ./ It was also thought, at one time, that the respiratory system differed qualitatively in unfertilized and fertilized sea urchin eggs, the cytochrome system being inoperative in the former and brought into play upon fertilization (Korr, 1939).…”