418 MR. B. THOMPSON LOWNE ON THE COMPOUND VISION 



Fig. 10. An optical section of a segment of the dioptron of Tipula in the recent condition. 



11. The spindle of the eye of the same, slightly altered by the process of preparation. 



12. A similar spindle. 



13. A segment or tube of a spindle from the same insect, showing the contracted tnbe with soft 



vacuolated material adhering to it, possibly a portion of its contents. 



14. a. A transverse section through the spindle of the same insect. 



14. b. A similar section, in which the peripheral tubes have partially collapsed. 



15. Three of the peripheral segments of the dioptron of a Blow-fly in the immature condition. 



16 to 18. Portions of the great rods of a Blow-fly, showing the different appearances which they 

 present, owing to partial or total collapse of the spindle. 



16. A portion of the spindle partially emptied by pressure. 



17. A specimen showing still further collapse of the tubes. 



18. A portion of a spindle showing vacuolation of the sheathing-eells and collapse of the tubes in 



normal saline solution. 



19. The lens at the outer end of the spiitdle from the same insect, from an osmic-acid preparation ; 



rate, spheroids in the interior of the lens, sp. spindle. 



20. A transverse section of the great rods, spindles, sp., sheathing-cells sh., and tracheal vessels, tv., 



from the same. 



21. The lcus-capsule, ruptured by pressure, from the Earwig. 



22. A single segment of the dioptron, and a few bacilla from the Yellow TJnderwing Moth (Triphcena 

 pronuba), from a specimen prepared in chloral hydrate solution. 



Plate XLI. 



Fig. 23. A section through the entire eye of a Noctuid (Xy/ophasia po/yodon). 



24. Transverse sections through the cone of the same insect : a, near the base ; b, near the apex, 



showing the coloured granules. 



25. Transverse sections through the rods and spindles of the same insect: a, b, c, three successive 



sections through the spindle-sheath ; d, section through the spindle showing the cells of the 

 sheath ; e, section through a stellate spindle. 



26. The chamber and cone of the same insect. The tube has collapsed. 



27. The tube between the cone and spindle, from the eye of a species of Noctuid Moth ; the tube 



contains unicellular parasitic organisms, z. 



28. The chambers and a portion of the spindles of two segments of the dioptron, an osmic-acid 



preparation from the eye of a Blow-fly : oc, outer portion of the cone ; cc , crystalline cone. 



29. The spindle from the same, mounted in a dilute solution of osmic acid. 



30. A section of the cornea of an African Carpenter Bee (Xylocopa), from a dried insect, showing 

 its laminated structure : c 1 , lenticular layer ; c 2 , laminated layer ; c 3 , inner surface. 



31. A single segment of the dioptron of an Ant (Formica rufa) , showing the ciliary rods cb. ; 31 a, one 



of the ciliary rods detached and more highly magnified. 



32. A similar preparation from the eye of a Wasp ( Vespa germanica) : 32 a, one of the same detached 



and more highly magnified ; cb 1 , refractive granule ; cP, iris cell ; cb 3 , fringe-like process. 



33. A portion of the eye of a Spider (Salticus scenicus), showing the fibrous membraue m, which 



separates the dioptric from the nervous structures ; Is, lymph-sinus, containing radiating 

 nucleated fibres. 



34. Two of the eyes of Salticus scenicus. 



35. The simple ocellus of a Blow-fly : 35 a, one of the retinal elements more highly magnified ; 

 r 1 , outer refractive segment ; r 2 , intermediate pigmented portion ; r 3 , nucleated protoplasmic 

 portion. 



