Which of the following is absent in the mouthparts of a housefly?

Which of the following is correctly described for a common cockroach $(Periplaneta \text{ } americana)$?

Answer in one word or one line. Where do you find Malpighian tubules?

Identify $P, Q$, and $R$ in the given diagram of the male reproductive system of a cockroach.

Read the following statements and choose the correct option:
$(A)$ The cockroach nervous system consists of a series of fused,segmentally arranged ganglia.
$(B)$ Ganglia are joined in the cockroach by paired longitudinal connectives on the ventral side.
$(C)$ The nervous system is present on the dorsal side of the cockroach.
$(D)$ In the cockroach,the total number of ganglia is nine.

What does '$X$' represent in the given figure?