470 SHAFER 



tonetes ignotus Walk., but speaks of the space nevertheless as 

 being formed by 2 hypodermal cells. 



Closely surrounding the entire length of the cone cells and 

 the hypodermal space are 20 to 22 secondary pigment cells 

 (Figs. 16, A, nsfi and B, sip). No primary pigment cells are 

 present. The distal ends of the secondary pigment cells touch 

 the cornea and their proximal ends are in contact with the 

 outer or distal retinula (Fig. 16, A, dm). It is proper to speak 

 of a distal retinula in this eye because there is also an inner or 

 proximal retinula -prn in each ommatidia — the 2 retinular parts 

 being connected by a very delicate strand (rs, Fig. 16, A). 

 Both proximal and distal retinulse are composed of 7 retinular 

 cells. Fig. 16, C, shows the 7 short distal retinular cells and 

 their nuclei. These cells surround the tip of the cone rosette 

 fashion. The proximal retinula is of about the same length as 

 the connecting strand. Fig. 16, D, shows the 7 nucleated cells 

 of this part in cross-section, and Fig. 16, E, is a similar section 

 near the middle part of a proximal retinula. The rhabdome in 

 its cross-section here is seen to be a 7-pointed star within a 

 circle which bears on its circumference 7-knobbed projections, 

 zv, radiating along the same lines as the points of the star and 

 lying between the boundaries of the retinular cells. The knobbed 

 parts, zv, are the secondary rods of Zimmer, 1897. This large 

 surfaced rhabdome terminates a little short of the outer end of 

 the proximal retinula in a single blunt rod tip as shown in Fig. 

 16, D. The outer end of the retinula therefore appears filled 

 with transparent liquid. Zimmer has described these transparent 

 ends in Cloe as " bladder trachea," and he figures no nuclei in 

 them. My sections of the turban eye of Callibcetis show the 7 

 nuclear structures present always, as represented in Fig. 16, D. 

 The inner faces of the distal retinular cells bear an extremely 

 thin rhabdome plate next to the tip of the cone (Fig. 16, C, drb). 

 Near the distal ends of the proximal retinula the connecting 

 strand, rs, breaks up, Fig. 16, A, into smaller strands which 

 seem to be continuous with the 7 secondary rods, zv of Fig. 16, 

 E. The connecting rods may be seen in the photograph no. 27. 

 The space around the rods, between the distal and proximal ret- 

 inulce, appears to be filled with an almost transparent liquid — 



