1. 1. Animals with a highly developed central nervous system have an almost similar composition of neutral lipids and fatty acids in all regions of the brain (grey and white matter) as does man. 2. 2. It seems also, from the point of view of the lipid state, that the degree of cerebralisation equal to that of man is attained by the dolphin and pilot whale. Man and dentated whale thus form the group of the highest order. The bearded whales, i.e. finback and humpbacked whale, assume the highest position of the middle group. 3. 3. In the young, differences in development are evident between the phylogenetically older and younger regions of the brain (e.g. cerebellum and cerebrum). 4. 4. The foetuses of whales and dolphins have a lipid and fatty acid composition equivalent to that of a one-year-old human child (physiological premature birth" of the human). 5. 5. The development of the brain lipids and fatty acids of man is complete after the fifth year of life. 6. 6. The lipid and fatty acid content of the human brain diminishes after the thirtieth year of life ("physiological degeneration"). © 1969."