FINE STRUCTURE OF VISUAL SYSTEM OF HONEYBEE (APIS MELLIFERA) .I. RETINA

A morphological study of the retina of worker honey bees as representatives of the closed-rhabdom type eye has been performed with the electron microscope. The ommatidia are composed of eight long receptor cells distributed in a circular pattern, each cell possessing an axon which extends to the optic lobe. Many microvilli form the individual rhabdomeres, which project toward the center of the ommatidium in two perpendicular directions to form the rhabdom. Rough endoplasmic reticulum and abundant mitochondria occur in the outer part of the receptors while in the inner part, near the rhabdomere, the cavities of a smooth form of the endoplasmic reticulum are enlarged to form wide cisternae. From distal to proximal ends, pigmented, nuclear, and fibrillar zones can be distinguished in the long axis of the retinula cells. In the fibrillar zone, microtubules appear. At the same level a particular receptor is detached from the ommatidium to form an independent axon. Overlying the receptors of a single ommatidium is a dioptric apparatus composed of a crystalline cone and a cuticular lens. The latter is a modified multilayered cuticule serving as a lens. The crystalline cone has a granular consistency and is enclosed by two modified pigment cells. Two other types of pigment cells are seen: (a) long pigment cells which run from the cuticule to the base of the retina; and (b) basal pigment cells, which are relatively short and located at the lower end of the rhabdom. The effect of dark adaptation and the functional significance of these findings is discussed. © 1969 Academic Press, Inc.