Mention the special features of the eye in a cockroach. Discuss the compound eye in arthropods and mention its structural features.

(N/A) $ \Rightarrow $ The eye of a cockroach is situated at the dorsal surface of the head in the form of black, kidney-shaped patches. It is a compound eye. Each eye consists of about $ 2000 $ hexagonal ommatidia.
$ \Rightarrow $ Each compound eye possesses a dioptric region and a receptor region. It is able to form different images of whatever it sees.
$ \Rightarrow $ Hence, a cockroach can receive several images of an object. This kind of vision is known as mosaic vision. From the inner end of each compound eye, thin nerve fibres emerge. They all unite to form the optic nerve, which connects to the brain.
$ \Rightarrow $ In arthropods, the compound eye is the primary visual organ. Its structural unit is the ommatidium. Each ommatidium consists of a corneal lens, crystalline cone, iris pigment cells, receptor cells (retinula cells), and a rhabdom, all supported by a basement membrane. These units work together to provide a wide field of view and high sensitivity to motion.