class of glycolipids is present in chlo­ roplast membranes and must surely be one of the most ubiquitous and abun­ dant natural substances in the world, thereby deserving the attention of lipid biochemists. It is therefore surprising to learn that in contrast to the glycosphingolipids, which were discovered in the 1870s, glycoglycerolipids were not discovered until the 1950s. Since that time investigations of the structure and distribution of these glycolipids have proceeded at an exponen­ tially increasing rate, and much information is now available for representa­ tives of many genera of bacteria, yeasts, algae, and higher plants. Glycoglyce­ rolipids have also been identified in animal cells, particularly in the brain, testes, and sperm.