Vanadium content of the eggs and embryos of ascidian, Halocynthia roretzi was determined by activation analysis. The determination
was performed by the comparison of the activity around 1.434 MeV peak of52V in the sample to that of the standard. The concentration of vanadium in the eggs remained unchanged during the cleavage
stage and the animal accumulated it progressively in the early embryogenesis. The content in the larvae after metamorphosis
amounted to nearly fifteen times of that of the unfertilized eggs.