— 36 — 



which the portion of the basilar membrane belonging to the 

 anterior surface is plane, not convex. In fig, 4, where the 

 retinulae are cut transversely, it is seen that the retinulae of 

 the anterior area of the eye {ret. v.) are placed much farther 

 from each other, than the retinulae of the dorsal surface of 

 the eye, which are closely adjacent to each other with "their 

 walls. Besides, even with low power as applied in this case, 

 it is noticeable that the axial lumen of the dorsal retinulae 

 is much wider than the lumen of the anterior ones. 



According to the characters just set forth all the retinu- 

 lae belonging to the anterior area of the eye may be sharply 

 enough delimited from the others in transverse sections 

 through the eye. 



All these facts bring us to the conclusion that the ante- 

 rior area of the eye possesses a peculiarly built retina, and 

 therefore deserves special treatment. 



We shall first turn to the histological particulars of those 

 retinulae that do not belong to the anterior area of the eye. 

 In a longitudinal section through the ommatidia (fig. 9) we 

 see that the retinulae (ret.) depart in a proximal direction 

 from the nuclei of the crystalline cells (n. s.). The distal re- 

 tinulae become wider and here are situated most of the large 

 vesicular nuclei {n. ret. 1—6) of the rhabdom cells. Towards 

 the basilar membrane (m. b ), i. e. proximally, the retinulae 

 narrow gradually. Proximally from the middle of the retinu- 

 lae it is possible to distinguish another, seventh nucleus 

 (n. ret. 7) of one of the rhabdom cells. The plasm of these 

 cells is light. The exterior surface of the retinula is covered 

 by a layer of finely granulated pigment [p. ret.). The inte- 

 rior axial lumen of the retinula is very wide but narrows 

 rather sharply distally, finally obliterating altogether; in the 

 proximal direction the lumen narrows very gradually and 

 reaches the basilar membrane. Along the walls of the axial 

 lumen are arranged the visual rods {rli.) intensely stainable 

 with eosin. The diameter of the latter is greatest at the distal 

 end, so that it seems— as if they wedge in with their ends 

 between the crystalline cells. 



The relations described are clearly illustrated in the dra- 

 wings of transverse sections made through the retinulae on 

 different levels (fig. 11—14). Figure 14 was taken at a high- 

 er magnification than the rest. 



