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FJQHT FIGURESPhosphorus holds a unique position in biological systems.It is not only present in a wide variety of biochemically important compounds, but has already been shown to be a key element in the biological activity of some of these compounds. The presence of phospholipids in cell membranes is well known. Phosphoproteins are abundant in egg yolk and in casein of milk. The nucleic acids, phosphorus containing substances, are receiving much attention today in relation to viruses, chromosomes and heredity. The elucidation of the vital role of phosphate ions in carbohydrate metabolism and in the energy transfers in muscle contraction is an important field of research.There have been many investigations of phosphate metabolism in adult tissues under widely varied conditions, but relatively little is known of phosphate metabolism in the embryo. Radioactive isotopes can be of great assistance in metabolic studies and fortunately tracer phosphorus, P32, is readily available, has a high energy of radiation and has a convenient half-life of two weeks all of which make this a useful trace element for biological work. This tool has been little used in embryological investigations as yet.In recent years several lines of investigation have suggested the value of a study of phosphate metabolism in early development utilizing tracer phosphorus. The findings of Barth and Jaeger ( '47a) that inhibition of development of the amphibian embryo by anaerobiosis, by sodium azide or by 429

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