LATERAL AND CENTRAL EYES OF SCORPIO AND LIMULUS. 193 



to the anterior intra-retinular cells. These lie about the middle 

 of the length of the retinulse, and are somewhat less compressed 

 than the anterior cells. They are seen as fusiform patches of 

 pigment in the section drawn in fig. 9 t. In fig. 10^ they are 

 seen more clearly, and in fig. 11 ^ and fig. 14 they are represented 

 diagrammatically. These we call the " median inter-retinular 

 pigment cells.^' They appear to have given origin to Von 

 Graber's " middle nuclei of the retinal sacs." 



Again, at the base of the retinulse, fitting to the rounded 

 ends of the nerve-end cells is a third series of pigmentiferous 

 cells, indicated by the letter v in the figures, whilst closely con- 

 nected with these is a wide-meshed reticulum of pigmentiferous 

 branching cells [to in the figures), which embraces the bundles 

 of intra-capsular nerve-fibres, and becomes continuous with 

 such masses of connective-tissue cells as those marked r in 

 figs. 8 and 10, and also forms junctions at intervals with the 

 pigmentiferous pavement cells which line the back of the 

 ommateal capsule (as shown in fig. 9). 



The three series of inter-retinular pigment cells and their 

 relation to the five nerve-end cells which build up a retiuula is 

 shown diagrammatically in the drawing (fig. 14). 



Eepresentations of actual preparations showing these con- 

 stituents of the retinal body are given in figs. 9 and 10. 



Central eye of Euscorpius Italicus, Ros. 



The central eye of Euscorpius, the structure of which is 

 illustrated by the section drawn in fig. 7, requires no special 

 description. The same elements are present as in Androctonus, 

 but the cells are relatively of larger size, and consequently 

 the retinulse and rhabdoms are fewer in number. 



We have not been able to study the distribution of the pig- 

 mentiferous tissue of the retinal body so fully in Euscorpius 

 Italicus as in Androctonus, owing to the treatment to which 

 the sections were subjected. 



It is noteworthy that post-nuclear phaospheres (fig. 7, k) 

 occur in the nerve-end cells of the central eye of Euscorpius just 



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