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

The correct option (which is the incorrect statement regarding the cockroach) is: A ring of gastric caeca is present at the junction of midgut and hind gut.

Let us analyze each statement step-by-step to understand why this is the incorrect characteristic:

1. Position of the Hypopharynx:
The mouthparts of a cockroach consist of a labrum (upper lip), a pair of mandibles, a pair of maxillae, and a labium (lower lip). A median flexible lobe, acting as a tongue, lies within the cavity enclosed by these mouthparts, which is called the hypopharynx. Thus, this statement is anatomically correct.

2. Genital Pouch in Females:
In female cockroaches, the 7^th sternum is boat-shaped and, along with the 8^th and 9^th sterna, forms a gynatrium or genital pouch (brood pouch). The anterior part of this pouch contains the female gonopore, spermathecal pores, and collateral glands. Thus, this statement is anatomically correct.

3. Anal Cerci:
In both male and female cockroaches, the 10^th abdominal segment bears a pair of jointed, filamentous structures called anal cerci. These structures are sensitive to vibrations and sound, serving as sensory organs. Thus, this statement is anatomically correct.

4. Position of Gastric Caeca vs. Malpighian Tubules:
In the digestive system of a cockroach, a ring of 6 to 8 blind tubules called hepatic or gastric caeca is present at the junction of the foregut and midgut (mesenteron) to secrete digestive juices.
In contrast, at the junction of the midgut and hindgut, there is a ring of about 100 to 150 yellow-colored, thin filamentous structures called Malpighian tubules, which function in excretion.
Therefore, stating that gastric caeca are present at the junction of the midgut and hindgut is incorrect.