Question

The image formed in the eyes of cockroach is

A. Apposition

B. Superposition

C. Both A and B

D. None of the above

Answer 1

The important sense organ of the cockroach is the compound eye. Cockroaches are nocturnal animals. In nocturnal insects, the image is formed by overlapping of images. It is a blurred image. A compound eye is a visual organ found in arthropods such as insects and crustaceans.

Complete answer:

The eye of cockroach is the compound type and is composed of many units called ommatidium. Insects have two kinds of ommatidia. The images formed in nocturnal insects like a cockroach in which the retinulae are present deep below the vitrellae and crystalline cone. The retinal sheath is absent. Therefore the rhabdome and retinulae of an ommatidium receive not only light rays that enter through its own cornea but also light rays that enter through the corneas of the adjoining ommatidia.

In nocturnal insects and many crustaceans the pigment is confined only around the cone cells, their retinulae and rhabdome do not touch the cone. Such eyes are called superposition eyes in which the ommatidia are not separated from each other by pigment. Superposition images are formed in dim light and are not sharp.

In diurnal insects the ommatidia are separated from each other by two pigment sheaths, their retinulae and rhabdome abut against the cone. Such eyes are known as apposition eyes in which only those rays of light can form an image which is parallel to the longitudinal axis of an ommatidium and pass directly through the center of the lens.

Hence, the correct answer to this question is option B.

Note: Cockroaches bear several types of receptor organs like other insects to perceive different types of stimuli like touch, smell, taste, sound, change in temperature, and light. The photoreceptors organs of insects are simple eyes or ocelli and compound eyes. But in cockroaches, usually, compound eyes are found.