Select the incorrect statement about Periplaneta americana.

The heart of Periplaneta is 13-chambered and lies along the mid-dorsal line of the thorax. The mandibles help in biting and chewing food, and the gizzard helps in grinding food (mechanical digestion). Exchange of gases takes place at the tracheoles by diffusion. The nervous system of the cockroach consists of nine segmental ganglia, three in the thorax and six in the abdomen.