Human Anatomy - Kotsan I. Y. 2009

Sense Organs
Organ of Vision (Eye)
Phylogeny of the Organ of Vision

Specialized morphological structures capable of perceiving light emerge at Cytology/cytology/16.html">Early stages of phylogenetic development. Light served as the primary stimulus that led to the evolution of a specialized visual organ in the animal kingdom. The core component of this organ across all animals consists of specific sensory Cells derived from the ectoderm, which are capable of responding to light stimuli. In most cases, these cells are surrounded by pigment, whose function is to channel light in a strictly defined direction and absorb stray light rays. In lower animals, such cells are scattered throughout the body.

During subsequent evolution, a pit lined with sensory cells (the retina) develops, connected to a nerve. In invertebrates, light-refracting media (the lens) evolve at the anterior part of the pit to concentrate light rays falling onto the retina. In vertebrates, whose eyes achieve the highest degree of development, additional structures emerge, including extraocular Muscles that move the eye, as well as protective apparatuses (eyelids and the Lacrimal Apparatus).

A characteristic feature of vertebrates is that the light-sensitive lining of the eye (the retina), which contains these specialized cells, develops not directly from the ectoderm, but as an evagination of the anterior cerebral vesicle.

At the initial stage of visual analyzer development (in fish), the peripheral end of the system (the retina) contains light-sensitive cells that are exclusively rod-like, while visual centers in the Brain are confined to the Midbrain. Such a visual organ is capable only of light perception and coarse object discrimination. In terrestrial animals, the retina acquires additional light-sensitive cells—cones—and new visual centers emerge in the Diencephalon, followed by the Cerebral Cortex in mammals. This evolutionary advancement enabled Color Vision, closely linked to the first signaling system. Finally, in humans, the higher visual centers in the cerebral cortex undergo exceptional development, giving rise to Abstract thinking associated with visual imagery, as well as written language, which constitutes a part of the second signaling system unique to humans.



Last update: 08/08/2026

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