BIOLOGICAL VISION has a dual character. It is designed to provide a comprehensive overview of the operation of the visual system of any animal (including humans) while simultaneously providing a guide to the larger work, PROCESSES IN BIOLOGICAL VISION. The latter work is currently available in draft form on the World Wide Web. The larger work provides a more comprehensive analysis of each subject addressed in BIOLOGICAL VISION. It also provides an extensive list of references in support of it. BIOLOGICAL VISION contains nine chapters. The first chapter begins with a phylogenic tree of the animal kingdom based on vision. The last ends with a series of figures defining the overall performance of the human visual system. Contrary to superficial statements in the recent literature, it shows that animals have enjoyed color vision for at least the last 500 years, long before the arrival of man. It also shows that biological vision is characteristically tetrachromatic; that is, it involves four separate and distinct spectral detection channels. The work takes a major step forward in showing that the human retina is also tetrachromatic, although the overall performance of the human visual system is partially blocked by the absorption of the lens system. The resulting human visual system is best described as a blocked tetrachromat. Its performance cannot be fully described using the conventional notion of humans as trichromats that dates from Thomas Young in 1802. Chapter Two addresses the three fundamental forms of eyes found in the animal kingdom. It shows the frequently defined dichotomies within the animal kingdom are inappropriate when discussing vision. The families of Arthropoda, Mollusca and Chordata exhibit unique visual features that justify the use of a trichotometric approach when discussing the phylogeny of vision. Chapter Three presents the overall architecture and signaling schematics found in animal vision. It defines the previously unrecognized role of the thalamus and other elements of the diencephalon in vision. It shows why the primary visual cortex does not play the primary role long envisioned in the literature. The primary role in the vision of the higher chordates is shown to be played by the thalamus. The thalamus is absolutely key to the ability of humans to analyze fine detail and to read. For the first time, the crucial role of the thalamic reticular nucleus in controlling the overall operation of the sensory systems of the organism is described. The chapter also shows the remarkable similarity between the signaling architecture of animal vision and its chief analog, the man-made system of color television. It also defines the multiple signaling modes involved in sensing and responding to the environment. These include the awareness, analytical, alarm and volition modes. The signaling path associated with the crucial analytical mode bypasses the primary visual cortex completely on its way to the cerebral cortex. Chapter Four focuses on the operation of the neuron in its various forms required to support the overall operation of the neural system. The internal electrolytic operation of the neuron is presented for the first time. This presentation includes the description of its signal amplifying mechanism based on the Activa. The Activa is the electrolytic liquid-crystalline semiconductor equivalent of the man-made transistor. The Activa being a three-terminal device results in a major redefinition of the fundamental morphological and physiological characteristics of the neuron. It is demonstrated that, while the neuron is the fundamental morphological element of the neural system, it is not the fundamental electrophysiological element. Individual sensory and signal projection neurons generally contain multiple electrophysiological elements operating in series. Chapters Five, Six and Seven focus on the unique characteristics, and close integration, of the photoreceptor cells, their associated retinal pigmented epithelium (RPE) cells and the inter-photoreceptor-matrix (IPM) between the two cell types. Chapter Five is devoted to describing the unique characteristics and operation of the photoreceptor cell from a multitude of perspectives. Like other sensory cells, it is shown to exhibit a neuro-secretory nature. In common with tactile sensory cells, it secretes a protein substance, opsin, used to produce the disks associated with it. Unlike, the tactile cells, the photoreceptor cells sense energy absorbed by the chromophores of vision rather than the energy due to bending of the individual hairs associated with the cells. The chromophores of vision are shown to originate in the RPE cells rather than, as previously thought, the photoreceptor cells themselves. Chapter Six reviews the photochemistry of biological vision and shows there are four (not three) chromophores associated with vision. The formation of these four chemical species within the RPE cells, and their delivery via the IPM, is examined in detail. Chapter Seven explores the morphogenesis of the chordate eye, with its reversed retina. It then explores the physical (cytological) dynamics of the photoreceptor cells. It shows that the so-called cones of vision are in fact immature or nonfunctional photoreceptor cells. This leads to the demonstration that all photoreceptor cells are morphologically rod-shaped and physically identical. They differ only in the type of chromophore used to coat their individual disk stacks. Chapter Eight addresses a variety of features of the visual system architecture not widely appreciated. A top level schematic of the entire visual system is provided along with a top-level functional diagram. These two diagrams support the computational anatomy employed to simplify the mathematical calculations required in the neural system. It is shown that computational anatomy frees the neural system from the need to perform transcendental arithmetic. Finally, the unique two-dimensional associative correlator employed within the perigeniculate nucleus/pulvinar couple to extract features associated with the imaged scene is presented. This couple is key to the abilities of higher chordates, to interpret fine detail (and in the case of homo sapiens, to read). Higher chordates in this context include nearly all chordate predators, including the predatory birds. Chapter Nine culminates in a summary of the performance achievable in human vision. The focus is on the five major performance characteristics. First, the transient response of the detection process. Second, the overall spectral performance (luminous efficiency function)of the visual system. Third, the chromatic (color rendition) capabilities of the system. Fourth, the dynamic sensitivity control (adaptation) capability of the system and the associated phenomenon of color constancy. And fifth, the temporal and spatial contrast performance of the system. For the first time, the complete photoexcitation/de-excitation mechanism and equation of visual sensing are described. It shows the equation, proposed by Hodgkin during the 1960’s as part of a piecewise solution, is actually a special case of the general mathematical solution. The special case of the long wavelength spectral channel is also developed. It is shown why the spectral performance of the visual system in the long wavelength region is lost as the scene illumination is reduced. For the first time, a cogent description of the transition from hyperopic, through photopic and mesopic to scotopic vision is presented. This description is compatible with all of the data in the literature going back to the 1930’s. Using the schematics presented earlier, the chapter provides a physiologically based Chromaticity Diagram for the first time. This three-dimensional diagram is shown to be conformal over the entire spectral range of the tetrachromatic eye. A two-dimensional simplification of this Chromaticity Diagram is presented that is adequate (with caveats) for most studies in human vision. This diagram leads directly to the definition of a unique color set sought by the vision community for many years. When transformed into the coordinate system of the CIE (1935) Chromaticity Diagram, the non-conformality and general limitations of that presentation are highlighted. The new Diagram also leads to a theoretically precise three-dimensional lightness-chrominance space for the first time. The resulting space uncovers several second-order problems with the similar Munsell Color Space. A brief section is presented on the mechanisms of perception and cognition. References are provided to the broader discussion in the larger work, PROCESSES IN BIOLOGICAL VISION.