How many spiracles are present in a cockroach (in $pairs$)?

Which of the following organisms has "ommatidia" as the unit of its eye?

Complete the following statement :
$(a)$ In cockroach,grinding of food particles is performed by ........ .
$(b)$ Malpighian tubules help in the removal of ........ .
$(c)$ The hindgut of the cockroach is differentiated into ........ .
$(d)$ In the cockroach,blood vessels open into spaces called ........ .

Gizzard (proventriculus) in cockroach lies between

In insects,the circulation of blood is .........

Select the incorrect option regarding the nervous system of a cockroach.