638 William Patten 



of the pieces is precisely the same. The inner faces of the arms of the 

 crosses are continuous with each other by means of a delicate hyaline 

 membrane (tìg-. 107), while the faces directed towards the enclosed 

 Squares are united by a series of fibres exteuding from the inner to 

 the outer surfaces of the crosses. From the centre of the inner surface 

 of each cross, a group of fibres projects inwards, and unites with the 

 connective tissue cells underlying the basai membrane (fig. 107, e. t.f.). 

 The enclosed Squares are bridged by a bündle of diagonal fibres 

 (figs. 106 and 110) which begin at the inner corner of the Squares, 

 as a single, round bar, and, after breaking up into two brush-like 

 bundles, extend outwards to the opposite corner, there becoming at- 

 tached along the tour lines a, è, e, d :tìg. HO). These diagonal fibres, 

 which maintain the same direction in ali the Squares , are of service 

 in orienting the arrangement of the ommatidial cells upon the mem- 

 brane. For convenience, we will call the vertical piane passing through 

 these fibres the diagonal piane of the eye; it coincides also with the 

 long diameter of the pedicel , but its relation to the body , I bave not 

 determined. The inner openings of the Squares are not rectangular, 

 but rounded, and reduced in size by the formation of a circular mem- 

 brane, thickest at the corners. If now, we study a series of very thin, 

 cross sections of the inner ends of the ommatidia, we shall be able to 

 determine the position that each celi occupies upon the basai membrane. 

 Beyond the base of the pedicel, and after the retinulae bave formed 

 the butterfly-shaped figure around the centrai and almost imperceptible 

 stalk (figs. 99 and 100), the retinulae suddenly separate, and the cen- 

 trai thread, increasing in size, soon dissolves into two groups of fibres 

 (figs. 106 and 1 10 r/l), which become attached to the inner surface of the 

 cross. One group is formed of two separate bundles, while the other is 

 apparently composed of two similar ones , so closely placed as to form 

 one figure, the configuration of which stili indicates its dual composition. 

 These four bundles , — of which one may discern the Impression upon 

 the crosses in macerated specimens, — are the four inner ends of 

 the retiuophorae, and the fibres are their root-like termina- 

 tions. 



If one follows the retinulae in the same manner, it will be seen 

 that after the Separation indicated in (fig. 101), the four cells, 4,6,5,7. 

 unite to form two pairs, each one of which occupies one angle of the cross, 

 on opposite sides of the diagonal plane (fig. 106). The three remaining 

 retinulae occupy that intervening angle from which the diagonal bar 

 arises, so that two cells are placed on one side of it, and the remaining 



