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William Patten 



different, main bundles. Besides the bundles of pigmented fibres, 

 there are likewise four colorless ones, which, arising from as many 

 main branches, ascend the four anglesof the cross and extend along 

 the outer surface of the four retinophorae (fig. HO n.f.). Lastly, a single, 

 minute, colorless brauch enters the base of the cross just below the 

 origin of the diagonal bar (fig. 108), and, describing a gentle curve, 

 issues from the centre of the opposite surface, to be continued straight 

 upward between the four retinophorae as the axial nerve fibre of 

 the ommatidium. In macerated specimens, one may see, in the centre 

 of the cross, the minute canal, from the round opening of which a small 

 nerve fibre often project». On the inner surface of the membrane, the 

 canal opens iuto a triangulär depression, situated on the very edge of 

 the cross, at the apex of the angle formed by the two sides (fig. 107 

 c.ax.f.). On Consulting the diagram (fig. 108), it will be seen that 

 the axial nerve fibre comes from the left band bündle, as does also a 

 group of fibres for the outside of one of the four retinophorae, the re- 

 maining three of which are supplied from the three surrouudiug 

 Squares; consequently the retinophorae are provided exterually with 

 nerve fibres from four main branches passing through four different 

 Squares. The retinulae of each ommatidium are similarly supplied 

 from three different branches, while the four bacilli of the pigmeut 

 cells receive their nervous supply from one and the same buudle. 

 The diagrammatic figure (fig. 108), represents a longitudinal sectiou 

 of the basai membrane, fig. 106, a tangential section of the same, and 

 finally, fig. 109, sections through one of the nerve bundles just beneath 

 the basai membrane ; they are supposed to represent the cells of the 

 same ommatidium with their nerve fibres, and consequently are desig- 

 nated with corresponding letters and figures, easily uuderstood by re- 

 ferring to the explanatiou of plates. Thus, althoiigh the ommatidia, 

 basai membrane crosses, and enclosed Squares, as well as the principal 

 nerve bundles , coincide in number, each ommatidium is supplied with 

 nerve fibres from four different bündle^, or, conversely, each 

 main bündle, instead of supplying a corresponding ommatidium, 

 divides into sixteen groups which supply the cells of four different om- 

 matidia. 



In macerated specimens, it is not a difficult matter to follow the 

 nerve fibres of each celi along its entire length. One always finds se- 

 veral fine fibres twisted about the bacilli, on account of their greater 

 size, more easily seen at the inner ends, where they may be observed 

 in cross sections, or in the isolated cells (fig. 111). They may be 



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