Metanephric kidney development in the chicken embryo: Glomerular numbers, characteristics and perfusion.
1. The urate, urea and ammonia content of the whole egg of the Japanese quail was measured in late incubation in eggs subject to different rates of water loss. 2. High rates of water loss substantially increased egg urate content, but had little or no effect on urea or ammonia content. 3. Allopurinol, an inhibitor of urate synthesis, reduced egg urate content to low levels, but produced no effect on urea content, and a small reduction in ammonia content. 4. The urea concentration of the embryo was lower than in allantoic fluid. 5. It is concluded that urate production by the avian embryo is primarily concerned with the modification of allantoic fluid composition.