Eye of Cockroach

Eye of cockroach

Cockroach is nocturnal, animal lives in damp and moist places where plenty of organic food is available.

In cockroach compound eyes because they are made up of repeating units, the ommatidium, each of which functions as a separate visual receptor.

The eyes are present on head situated dorso- laterally. The eyes are black and kidney shaped.  The outer surface of eyes is covered by transparent cuticle known as cornea.  The cornea is divided into large number of hexagonal facets like honey comhe like structure. Below  facet, there is presence of ommatidium inside the eyes. 

The ommatidia are the visual elements and there  are about as many as 2000 ommatidia are present.  Each ommatidium has a biconvex lens forms cornea which is formed by transparent and thickened cuticle. The lens is formed of two corneagen cells which are derived from epidermis. Below the corneagen cells there is presence of transparent crystalline cone act as second lens surrounded by four cone cells or vitrallae.  The part of cornea up to the most extreme inner end is known as dioptrical region, which focous light upon receptor region attached to inner end of cone.

Eye of cockroach shows presence of spindle shaped refractive bodies called as rhabdom which is made up of seven elongated units called as rhabdomeres. The are surrounded by photoreceptor cells which are also seven in numbers. The photoreceptor cells are elongated also called as retinulae or retinular cells secreted by respective rhabdom. The rhabdoms and retinular cells togather forms receptor region which is rest on basement membrane.  At the base of retinuar cells sensory nerves are present which joins to the brain. 

The cone cells are surrounded by pigment cells laterally, which forms an iris pigment sheath. While pigment cells surrounding rhabdom and retinular cells from all side produces sheath called retinular pigment sheath.

In eye of cockroach each ommatidium is separated from each other by iris pigment sheath and retinular pigment sheath. Hence such eye is called as opposition eye in which image formation is take palce only when light ray passes in longitudinal axis of an ommatidium through center of lens and reaches to the visual cells.

In the eye of cockroach each ommatidium forms a separate  image but images are adjacent to each other. All ommatidia  produces an image called  opposition image and the vision of such eye is called mosaic vision.