Fig. 3. Histological sections of control blastogenic stage D primary and secondary buds (A,C,E,G) as compared to 6 mg BHT l^-1-treated primary and secondary buds after 10 days exposure, on third day of arrested stage D (B,D,F,H). Azan Heidenhains stain. (A) Control ramet, primary bud at blastogenic stage D. Only a few cells can be seen in the bud blood vessels. (B) BHT-treated primary bud after 3 days arrested at blastogenic stage D. The bud periphery blood vessels are thick and packed with enormous numbers of cells. (C) Enlargement of the endostyle area in the primary control bud; only few blood cells can be seen near the endostyle epithelium. (D) The endostyle of the treated primary bud, surrounded by an unusual mass of cells. (E) A few cells circulating in the peripheral blood vessel of the primary control bud and the lacunas around its digestive system. (F) Large numbers of blood cells circulating in the treated primary bud peripheral blood vessel and its digestive system. (G) Secondary bud control ramet has large empty spaces (subdivisions of the future organs) lined by epithelium of thin blood vessel. (H) BHT-treated secondary bud has dilated blood lacuna filled with m any cells. b, bud; bs, branchial sac; bv, blood vessel; ds, digestive system; en, endostyle; s siphon; sb, secondary bud.