Paraffin sections of air respiratory organ of catfish measured 26.3 (A), 24.6 (B, D), 20.9 (C) cm in length, stained with H&E. The thin arrows refer to areas of vascular and perichondrial CT invasion into the cartilage. The thick arrows refer to epithelial invaginations. The red asterisks refer to divisions of cartilaginous units. Scale bars represent 50 μm in "A", 80 μm in "B-D".
