Which one of the following statements is incorrect ?

The pancreas contains Islets of Langerhans, which have two main types of cells: $\alpha$-cells and $\beta$-cells.

The $\alpha$-cells secrete the hormone glucagon, which increases blood glucose levels by stimulating glycogenolysis.

The $\beta$-cells secrete the hormone insulin, which decreases blood glucose levels.

Therefore, the statement that $\alpha$-cells secrete insulin is incorrect.

Answer: $\alpha$-cells of pancreas secrete insulin