The fine structure of a nauplius eye

Abstract

The nauplius eye of the cyclopoid copepod Macrocyclops albidus has been studied by means of the electron microscope. It is composed of 1 ventral and 2 dorsal ocelli. Each dorsal ocellus consists of a large, pigmented cell, 2 tapetal cells which form a hemispherical cup and are tightly packed with crystals, 9 retinula cells and 5 conjunctival cells. The retinula cells have large masses of endoplasmic reticulum, which can be found in two distinct distributional states, also numerous bodies composed of variously coiled membranes, large amounts of glycogen, mitochondria and scattered neurotubules. The light-sensitive brush borders of these cells are closely coapted and form the irregularly shaped rhabdome. Each of the 9 retinula cells sends an axon by one of three routes to the protocerebrum. In addition, a dendrite emerges from the protocerebrum, enters the ocellus and ends blindly in immediate vicinity to the rhabdome. The observations concerning the structure of the eye made in the present study have been compared to those of light microscopical investigations. Comparison of structure and probable function of the nauplius eye and other arthropod eyes has led to consideration of the probable mode of synaptic transmission between primary and secondary sensory neurons in the ocellus, i.e. between retinula cells and eccentric cell dendrite, and various morphological features that might be of importance in this connection.