neio Type of Compound Eye. 235 



In several species of Gymothoidce I have heen able to recog- 

 nize the presence of these same hyaline cells both in sections 

 and in teased preparations : I invariably found two present, 

 and tlieir relation to the retinula-cells and to the rliabdom 

 was precisely as described above in Serolis. ^ya, however, 

 agrees with Gymothoa and other Isopods and differs from 

 Serolis in the fact that there are seven cells to each retinula ; 

 but in the presence of these remarkable hyaline cells, as well 

 as in their structure and position, yEya exhibits a striking 

 resemblance to Serolis, and differs, so far as our knowledge 

 goes, from all other Isopods. This structural resemblance 

 between yEya and Serolis tends further to confirm the view, 

 held by many carcinologists, of the close relationship between 

 the Serolidse and Gymothoidse. 



In one of my figures of the structure of the eye in Serolis 

 Schythei (loc. cit. pi. ix. fig. 5) I have depicted the rliabdom 

 as ending in a fine filament which passes through the hyaline 

 cell as far back as the membrane which bounds the omma- 

 teum posteriorly ; I have also (figs. 3, 4) noted a similar 

 prolongation of the rliabdom in Serolis cornuta. 



On again referring to my preparations of both these species 

 I find that those figures are not quite accurate. In Serolis 

 Schythei the rliabdom has not the conical form which I have 

 erroneously given to it in my drawing ; it ends in four blunt 

 points {cf woodcut) : just below the termination of the rliab- 

 dom is a bundle of delicate fibrils which unite into a single 

 fibre {r) ; this passes through the substance of the hyaline cells 

 and can be traced back as far as the ommateal membrane. 

 In S. cornuta the arrangement is identical. 



In some young examples of S. Schythei, taken from the 

 brood-pouch of the mother, this bundle of delicate fibres, ter- 

 minating in a single long fibre, was present, and appeared 

 from its position to be a product of the four pigmented 

 retinula-cells. At this stage the thickened masses which 

 form the greater portion of the rhabdom in the adult eye were 

 not developed. If it were not for this fact the bundle of 

 fibrils (r in woodcut) in the adult eye would seem to have 

 nothing to do with the rhabdom of the pigmented retinula- 

 cells, but to be anteriorly formed by the hyaline cells. It is 

 indeed quite possible that it is in part formed by these cells. 

 If this be so, the retinula in Serolidge and Cymothoidse is 

 composed of six cells, two transparent cells surrounded by 

 four pigmented cells, all of which secrete chitinous rods. The 

 central transparent cells, however, do not appear to end in 

 nerve-fibres, unless the axial chitinous rod contains nerve- 

 fibrils, which is of course a mere suggestion. 



16* 



