[Distribution of acid phosphatase in the chicken blastoderm]

The distribution of acid phosphatase in the chick blastoderm (stages 2--4 by HH) has been studied using cytochemistry. A marked increase of enzymatic activity all over the blastoderm was shown to coincide with the beginning of primitive streak formation. A part of the cells after their immigration are characterized by the fall of acid phosphatase activity. The percentage of such cells increases in the cranio-caudal direction of the definitive primitive streak. The patterns of yolk utilization upon the separation of individual embryonic rudiments are discussed.