During the evolution of vision, some animals have quite complex optical devices. These, of course, include compound eyes. They formed in insects and crustaceans, some arthropods and invertebrates. What is the difference between a compound eye and a simple one, what are its main functions? We will talk about this in our material today.
Composite eyes
This is an optical system, raster, where there is no single retina. And all the receptors are combined into small retinules (groups), forming a convex layer that no longer contains any nerve endings. Thus, the eye consists of many separate units - ommatidia, combined into a common system of vision.
Composite eyes, inherent, for example, in insects, differ from binocular ones (inherent in humans as well) by poor definition of small details. But they are able to distinguish light vibrations (up to 300 Hz), while for a person the limit is 50 Hz. Also the membranethis type of eye has a tubular structure. In view of this, compound eyes do not have such refractive features as farsightedness or myopia, the concept of accommodation is not applicable to them.
Some features of the structure and vision
In many insects, the organs of vision occupy most of the head and are virtually motionless. For example, the faceted eyes of a dragonfly consist of 30,000 particles, forming a complex structure. Butterflies have 17,000 ommatidia, a fly has 4,000, and a bee has 5. A worker ant has the smallest number of particles, 100.
Binocular or faceted?
The first type of vision allows you to perceive the volume of objects, their small details, to estimate the distance to objects and their location in relation to each other. However, human binocular vision is limited to an angle of 45 degrees. If a more complete view is needed, the eyeball moves at a reflex level (or we turn our head around the axis). Compound eyes in the form of hemispheres with ommatidia allow you to see the surrounding reality from all sides without turning the organs of vision or the head. Moreover, the image that the eye transmits in this case is very similar to a mosaic: a single element is perceived by one structural unit of the eye, and together they are responsible for recreating the complete picture.
Varieties
Ommatidia have anatomical features, as a result of which their optical properties differ (for example, in differentinsects). Scientists define three types of facet:
- Apppositional. Diurnal insects have such complex compound eyes. A pigment that does not have transparent properties separates facets - particles that are nearby. And the eye receptors can only perceive light that coincides with the axis of a particular ommatidium.
- Opticosuperposition. Some crustaceans, as well as nocturnal and crepuscular insects, have such complex compound eyes. The pigment contained in the eye alternately insulates the ommatidia by moving, which increases the sensitivity of the organs of vision in low light.
- Neurosuperpositional. Various ommatidia summarize the signal coming from the same point in space.
By the way, some species of insects have a mixed type of faceted organs of vision, and many, in addition to those we are considering, also have simple eyes. So, in a fly, for example, paired facet organs of rather large sizes are located on the sides of the head. And on the top of the head there are three simple eyes that perform auxiliary functions. The same organization of the organs of vision and the bee - that is, only five eyes!
In some crustaceans, compound eyes seem to sit on mobile outgrowths-stalks.
And some amphibians and fish also have an additional (parietal) eye, which distinguishes light, but has object vision. Its retina consists only of cells and receptors.
Modern scientific developments
Recently, compound eyes are the subject of study andthe enthusiasm of scientists. After all, such organs of vision, due to their original structure, give rise to scientific inventions and research in the world of modern optics. The main advantages are a wide view of space, the development of artificial facets, used mainly in miniature, compact, secret surveillance systems.
