THE EYE OF THE PARASITIC COPEPOD, SALMINCOLA EDWARDSII OLSSON (LERNÆOPODA EDWARDSII OLSSON)

Abstract

1. The eye of Salmincola edwardsii Olsson is located medianally, in the space between the brain and the dorsal wall of the body. 2. Unlike the eye of Achtheres ambloplitis Kellicott another one of the Lernæopodidæ, described by Wilson, the visual organ of Salmincola edwardsii is normally developed and functions during the first copepodid or the free-swimming larval stage of the parasitic organism. 3. The eye is more or less of a reddish-brown, x-shaped pigment blotch, consisting of three ocelli. Two ocelli are located laterally, while the third is below these, occupying a median position. 4. In size, the median ocellus is about two thirds the dimensions of either of the lateral ones. 5. Each ocellus is constructed somewhat similarly. It is embedded in a semi-lunar cup whose internal surface is thickened into a basal plate. Covering the external face of the ocellus is a cuticle which is divided up into squares that appear like the facets of ommatidia. 6. Interiorly every ocellus contains numerous retinal cells. There are nine of these cells in each lateral ocellus and five of them in the median ocellus. 7. The retinal cell possesses a large, rounded nucleus and a single rod-like, heavily staining phaosome, which is located between the nucleus and the basal plate. 8. The optic nerve which makes its way from the ocelli to the brain consists, in all probability, of twenty-three nerves corresponding to the number of retinal cells found in the eye.