Fig. 4. (A) Gross morphology of thyroid glands examined at stage G42 of
B. gargarizans larvae in control groups. Thyroid gland (arrow) was located on both
sides of urobranchial cartilage. Scale bar for A is 100 lm. Ge. Geniohyoideus; Co.
Copula II. Comparative thyroid gland histology of B. gargarizans larvae exposed to
control groups (B) and 100 mg/L NO3–N groups (C) at stage G42. Each scale bar
corresponds to 50 lm. Th. Thyroid gland; Col. Colloid.