472 SHAFER 



1. The cornea of the turban eye of the smaller species is 

 thinner and its lenses less convex than those in C. hageni. 



2. The retinular connecting strands in the eye of the smaller 

 species are about one and one third times longer than the prox- 

 imal retinulee. That is, the strands in this species are relatively 

 a third longer than they are in the eye of C. hageni. 



DEVELOPMENT OF THE LARGE FACETTED EYE 



AREA (TURBAN EYE) IN CALLIB^STIS Etn., 



AND IN SYMPETRUM CORRUPTA Hagen. 



As is well known, the young of dragonflies and mayflies 

 pass through incomplete metamorphoses in their post-embry- 

 onic development, and the young of both live in fresh water. 

 Young nymphs of both species of Callibcetis and of S. cor- 

 rufita were collected from still or slowly running water near 

 Stanford University in March and reared to the adult stage in 

 the laboratory. In this way material was obtained representing 

 different stages in the development of the large facetted-eye 

 areas. Carriere, 1886, first briefly called attention to the origin 

 of the elements of the turban eye of mayflies from elongated 

 epithelial cells near the dorsal edge of the lateral eye. His 

 observations in the main agree with the following account. 



All nymphs of Callibcztis under 4 mm. in length have only 

 lateral pigmented eyes. When the nymphs are 4 to 5 mm. long 

 however, the lateral eyes have about completed their develop- 

 ment. Then a narrow yellowish or light brown band appears 

 above the dorsal edge of each lateral eye of the male nymphs. 

 This marks the first noticeable beginning of the large facetted 

 eye, and cross-sections made of the head of such a nymph show 

 the hypodermis, just beneath the light brown band, to be made 

 up of modified long slender hypodermal cells with a second 

 layer of much shorter cells lying against their inner bases. 

 Already 2 membranes very close together are forming here. 

 One of these membranes (Fig. 21, A, k), marks the inner bound- 

 ary of the second layer of cells A, 2J111. The other membrane 

 A, dm, marks the inner boundary of the outer layer of modified 

 long hypodermal cells. The nuclei of some of the cells of the 

 second layer are above the membrane A, bm, and some are 



