A large single “cornea” is situated on the frontal side of the naso of Microcaeculus. Caudally and nearly coaxial to the cornea separated by a hemolymphatic cavity, are the two median eyes on the other side of the naso. They face the bases of the cheliceres, directed caudally. The cuticle of the eye attains a thickness of up to only 0.24 μm. Sensory cells protrude from the eye cup in a dorsal direction delivering axons of different diameters bent caudally toward as yet undetermined centers. Each eye consists of 6 retinula cells, covered by a thin epithelial layer, and of an undetermined number of sheath cells. Different zones can be distinguished schematically in the sensory cells: 1. Rhabdomere Zone. Directly beneath the cuticle and the cuticle-forming cells, rhabdomeres are spread superficially; their corresponding plasmatic regions, also located here, contain much smooth- and rough-surfaced endoplasmic reticulum (ER), some multivesicular bodies, mitochondria, centrioles, and α-glycogen. 2. Microtubuli Zone. This zone is characterized by many microtubules. Few rough-surfaced ER, but many mitochondria, are present in this zone; voluminous ER cisterns are to be found placed in the cell area facing the hemolymphatic cavity. 3. Nucleus Zone. Due to an increased cell volume in this zone, the eyes overlap over a large area. In the sensory cells a conspicuous massing of glycogen rosettes, as well as several organelles, is to be found. 4. Axon Zone. The axons are of varied diameter (0.7–1.8 μm). Large amounts of glycogen are found only in thicker axons, cross-structured by single smooth ER-cisterns. Electron-microscopic investigations confirmed the findings of Coineau (1970). Additional probabilities are presented and discussed in regard to other functions of these eyes. As to the structure of the eyes, a perception of differences in light intensity is probable. Image vision seems an impossibility, as only 6 retinula cells exist in each eye. However, a certain “perception of light direction” may be possible since the field of view is limited by the body and its dorsal ledge.