1905.] NATURAL SCIENCES OF PHILADELPHIA. 157 



Explanation of Plates VI, VII, VIII. 



Plate VI, Fig. 1. — Section of entire eye and optic lobes. The heavy lines show 

 the course of the nerve fibres as worked out by Kenyon (diagram- 

 matic) . 



Plate VII, Fig. 2. — Ommatidium of young pupa before rhabdome is differenti- 

 ated and at time of first pigmentation of retinula cells. 



Fig. 3. — Ommatidium of older pupa, showing differentiation of rhabdome 

 and lens formation. 



Fig. 4. — Cross-section through distal end of cone of pupa of same age as 

 fig. 2, showing corneal pigment cells. 



Fig. 5. — Cross-section through cone of older pupa. 



Fig. 6. — Cross-section through proximal end of cone of pupa (same stage 

 as figs. 3 and 5). 



Fig. 7. — Cross-section through cone of young pupa. 



Fig. 8. — Cross-section through retinula of young pupa before rhabdome 

 formation. 



Fig. 9. — Cross-section through distal end of retinula of young pupa, show- 

 ing first traces of pigment. 



Plate VIII, Fig. 10. — Entire ommatidium (somewhat diagrammatic). Adult. 



Fig. 11. — Entire ommatidium, as if dissected out, without outer pigment 

 cells (diagrammatic). Adult. 



Fig. 12. — Section of entire ommatidium, showing distribution of pigment. 

 Adult. 



Fig. 13. — Cross-section just proximal to lens, slightly oblique. 



Fig. 14. — Cross-section through extreme distal ends of retinulse and proxi- 

 mal ends of cones, slightly oblique. 



Fig. 15. — -Cross-section through retinulse, showing relation of outer pigment 

 cells in tliis region. 



Fig. 16. — Cross-section through retinula; in region of nuclei. 



Fig. 17. — Cross-sect'on through retinulse in region of proximal nucleus. 



Fig. 18.— Cross-section of eye, cutting basement membrane parallel. Tlie' 

 distinctness of nerve fibres of each ommatidium is shown. 



