Which of the following characteristics is incorrect with respect to cockroach ?

To determine which characteristic of the cockroach is incorrect, let us analyze each of the options step-by-step:

1. Position of gastric caeca:
In a cockroach, a ring of 6-8 blind tubules called gastric or hepatic caeca is present at the junction of the foregut and midgut, not the midgut and hindgut. At the junction of the midgut and hindgut, a different set of structures called Malpighian tubules (around 100-150 yellow-colored thin filamentous tubules) is present, which helps in excretion. Therefore, the statement "A ring of gastric caeca is present at the junction of midgut and hind gut" is incorrect.

2. Hypopharynx:
The hypopharynx acts as a tongue-like structure in cockroaches and lies within the cavity enclosed by the mouthparts. This statement is correct.

3. Female genital pouch:
In female cockroaches, the 7^th sternum is boat-shaped and together with the 8^th and 9^th sterna, it forms a genital pouch (or gynatrium). This statement is correct.

4. Anal cerci:
In both male and female cockroaches, the 10^th abdominal segment bears a pair of jointed filamentous structures called anal cerci. This statement is correct.

Thus, the incorrect characteristic is that gastric caeca are present at the junction of the midgut and hindgut.