476 



SHAFER 



extra retinulae are found in a ring around the outer margin of 

 the eye. This has been noted by Pictet, and figured by 

 Zimmer, 1897, and named by them the " abkonical ring" in 

 the adult eye. 



Fig. 20 shows the structure of 2 ommatidia from the turban 

 eye of an unidentified mayfly. It has primary pigment cells. 

 No adults of this species were reared, but the development of 

 the eye up to the sub-imago stage is, in general, identical with 

 the development of the eyes just described. 



TABLE OF MEASUREMENTS OF DIVIDED-EYE ELEMENTS. 



Small pigmented 

 Ommatidia. 



Length. 



Greatest 

 Diameter. 



Greatest 

 Thick- 

 ness. 



Large Ommatidia. 



Length. 



_ , ! Greatest 



Greatest Thick . 

 Diameter. 



Corneal lens 



Hypodermal space. 



Cone 



Entire retinula 



Proximal retinula. 



0.348 

 1.268 



I 0.07 I 

 measured along the cone axis. 



0.125 



ness. 

 mm. 



0.158 



0.19 



6. Callibcetis calif or?iica Banks. 



Cornea 



Hypodermal space. 



Cone 



Entire retinula 



Proximal retinula.. 



0.09 

 .126 



