Question

Apposition image in insects is formed during
A. Bright light
B. Dim light
C. Both A and B
D. None of the above

Answer 1

The Apposition eyes were almost definitely the original compound eye type and are the oldest known fossil eyes, found from the Cambrian Period trilobites. While arthropods, in particular insects and crustaceans, are most commonly associated with compound eyes, compound eyes formed separately in two other phyla, the molluscs and the annelids.

Complete Answer:
- In arthropods, the compound form of eye is located. A compound eye has an appearance-like network.
- It's made up of minute lenses called ommatidia. With the assistance of the lenses, the eye may shape either apposition images or superposition images. In the case of an apposition eye, each ommatidium orients only rays coming from the bright light which are almost parallel to its long axis.

The picture of the whole is the product of a combination of the images of these pieces.
1. These images arc formed like houseflies in diurnal insects in which the retinular lie immediately below the crystalline cone and vitrellae.
2. A dark pigmented sheath called the retinal sheath covers them, which absorbs light rays and avoids them from transferring them to the adjacent ommatidium.
3. The iris sheath wraps the crystalline cone. Accordingly, only light rays entering the ommatidium cornea converge on the rhabdom.
4. Thus, in each ommatidium, a small separate image of a part of the object is created.
5. The overall image created in the compound eye is a mosaic of a few small pictures.
Such an image is referred to as an apposition image because it is created in each of the ommatidial by a juxtaposition of small discrete pictures. This sort of vision is called the vision of mosaics.

- The sensory cells of the ommatidium will pick up light from a wide part of the visual field in the superposition eye. The image received can overlap with the image received. Thus, the image of the superposition increases in brightness but lacks sharpness compared to the image of the apposition. Diurnal insects have apposition representations because they are generated in bright light by these representations.

The correct answer is option (A) Bright light.

Note: Each compound eye is made up of 2000 ommatidia. Ommatidia are structural and functional units or visual units of the compound eye.