THE EYE OF SALMINCOLA EDWARDSII OLSSON. 4! I 



Within every retinal cell, there is a prominent nucleus, more 

 or less spherical in appearance (Figs. 4 and 5, n), which is made 

 up of a network, consisting of fine chromatic strands with thick- 

 ened clumps of chromatin. At the base of the cell, that portion 

 nearest the basal plate of the ocellus, there is a rod-like, heavily 

 staining, structure surrounded by a clear space. This is the 

 phaosome (Figs. 4 and 5, /), and in all probability it functions 

 in the transmission of visual stimuli to the nerves of the retinal 

 cells. Esterly found numbers of these bodies distributed ran- 

 domly through the retinal cells of Eucalanus elongatus. In 

 Salmincola edwardsii, however, this was not found to be the case. 

 Here there is but one phaosome to each retinal cell and this 

 occupies a definite position between the nucleus and the basal 

 plate of the ocellus. No definite lenses are present in the ocelli 

 of Salmincola edwardsii. 



The nerves of the retinal cells make their way posteriorly, 

 from the surfaces of the semi-lunar cups. These nerves are 

 very thin, fine strands which cannot be counted with even the 

 highest powers of the microscope. But assuming that each 

 retinal cell is connected with one nerve, there must be nine 

 retinal nerves to each lateral ocellus, and five of them to the 

 median ocellus, making altogether twenty-three nerves. Slightly 

 back of the ocelli, these nerves combine into an optic nerve (Fig. 

 5, o. 7?) and this then enters the brain of the larval organism. 



SUMMARY. 



1. The eye of Salmincola edwardsii Olsson is located median- 

 ally, 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 Lernaeopodidae, 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 pig- 

 ment blotch, consisting of three ocelli. Two ocelli are located 

 laterally, while the third is below these, occupying a median 

 position. 



