The Energy-Sources in Ontogenesis

Abstract

1. Investigation of the ammonia content of the developing hen's egg shows that though in absolute amount it steadily increases during incubation, in percentage of the embryonic weight it declines. 2. The intensity of production of ammonia reaches its highest point on the fourth day, i.e. five days before that of urea production, and seven days before that of the production of uric acid. 3. The absolute amounts of nitrogen excreted in the form of ammonia are so small, however, that the curve for protein combusted by 100 gm. of embryo each day is hardly affected, and rises to a peak between the eighth and ninth days. 4. These results are compared with others already in the literature of chemical embryology, which seem to bear on the theory of recapitulation. They afford further support to the conception of an ontogenetic succession of energy-sources.