29G S. WATASE. 



animals; nevertheless, witli care one can easily make them out. 

 Beneath the corneagen conies the stratum consisting of two cells, 

 the vitrellae, which secrete an enormous cuneiform, chitinous 

 structure, the crystalline cone {r. c) with its more pointed end 

 turned inward. The crystalline cone consists of halves, each 

 corresponding to a single vitrella cell which secretes it on its 

 median, axial surface. The lino x, as in Serolis, shows the 

 morpliological lumen of the omniatidial cavitj'. 



Next below this stratum comes the group of four cells, the 

 retinulae (/?/). Tlie chitinous edges of the retinulae meet in the 

 median axis and form the rhabdom {lih). Transverse striations, 

 rather broad and coarse in tlieir nature, are seen through the 

 transparent cuticle, tlie rhabdomere. At the lower part of a 

 retinula cell, near the basement membrane, is situated its nucleus 

 (n); it may be found below the membrane. 



The retinula cell undergoes a curious modification at the upper 

 end. Each of the retinula cells sends out a flattened process 

 which is highly pigmented and which completely ensheaths the 

 dioptric portion of the onimatidium from the outside. In fact, 

 the place of pigment cells {pg. c) in Serolis is taken by the 

 modified upper expansion of the retinula cells. Outside of this 

 pigmented sheath there exists a number of non-pigmented, 

 elongated ectodermal cells {p.c) which pack the interspaces 

 between the adjacent ommatidia. 



If we plot out the whole structure into a diagram, in the same 

 "way as we did the ommatidia of Serolis, it will assume the 

 appearance shown in Fig. 3a, PI. XXIX. The innermost cells, 

 the "hyaline cells" oi S&i'olis, are not represented; the cells in 

 the second circle are greatly developed {Rt), meeting one another 

 with their chitin-sccreting edges, the rhabdomeres, while the 

 upper extremity of each retinula cell envelops the crystalline 

 cone from the outside, thus physiologically taking the place of 

 pigment cells, {pg.c) or 5 in Serolis, Fig. lb, PI. XXIX. 



In the third circle the two vitrellae are found with their chitin- 

 secreting surface marked yellow. The cells in the fourth circle 

 constitute the corneagen (c. g). The fifth circle of cells is 

 represented by the packing cells {jf. c). 



