LATERAL AND CENTRAL EYES OF SCORPIO AND LIMULUS. 183 



The nerve-end cells of the ommateum of a lateral eye of 

 Androctoiius funestus are muchlarger than the neighbouring 

 indifferent cells. They are elongated, and are disposed somewhat 

 radially, reaching from the lower surface of thecuticular 

 lens to close upon the ommateal capsule. The nucleus is placed 

 near the capsular or filamentary extremity (that which is 

 connected with the nerve filament) of the nerve- end cell, and 

 is of large relative size, spherical, and with well-marked 

 nucleolus. The nerve-end cells appear to possess over their 

 whole surface a well-marked cuticular substance which encloses 

 the soft protoplasm. The minuter structure of these cells we 

 are not prepared to discuss on the present occasion, our object 

 being morphological rather than histological. A very important 

 feature in the structure of the nerve-end cells is the existence 

 of a special rod-like cuticular thickening on the side of each 

 cell. This thickening is highly refringent, and very possibly 

 is of a chitinous nature, though we are unable to offer any 

 evidence as to its chemical nature. In the section drawn in 

 fig. 2 fragments of these lateral hard-pieces are seen of a 

 yellow colour (i). It appears, from further examination of 

 sections, that the lateral thickening in each nerve-end cell 

 is so placed as to adjoin and even fuse with the similar lateral 

 piece of a neighbouring nerve-end cell. The resulting hard- 

 piece has been called by Grenacher, when observed in the 

 compound eyes of Insects and Crustaceans, a '^rhabdom." 

 We may make use of the same term for the composite body 

 formed by the union of the lateral hard-pieces of the nerve-end 

 cells of the Scorpion's eye. At the same time, each hard- 

 piece in a nerve-end cell may be called a " rhabdomere." 



The rhabdoms of the lateral eye are not so well developed as 

 those of the central eye. They appear to be irregular in 

 shape, and inconstant in the number of cells and rhabdomeres 

 which take part in their formation. They will be best under- 

 stood when the structure of the central eye has been de- 

 scribed. 



The indifferent cells of the ommateum of a lateral 

 eye of Androctonus funestus are to be distinguished into 



