AND THE MORPHOLOGY OF THE EYE IN INSECTS. 419 



Fig. 36. One of the confound ocelli of a Noctuid caterpillar : h, hypoderni ; py, pigment covering the 

 spindle. 



37. One of the compound ocelli from another Noctuid caterpillar. 



38. A similar preparation from a third species of Noctuid caterpillar : no, union of three nerve- 

 trunks from three compound ocelli. 



39. An oblique section through a similar eye in an embryonic condition. 



40. A transverse section of a compound ocellus from a Noctuid caterpillar, showing the iris and lens 



in situ. 



Plate XLII. 



Fig. 41. A transverse section through the entire eye of a Dragon-fly (Ayrion viryo), from the perfect 

 insect. 



42. A highly magnified representation of a portion of the retinal ganglion, from the same prepa- 

 ration : ii l , nuclear layer; cl x , cellular layer; f 1 , fibrous layer; cl 2 , second cellular layer; f 2 , 

 second fibrous layer ; n 2 , second nuclear layer ; x, second decussating layer of fibres. 



43. A section through the entire eye of a larval Ayrion, from a specimen 6 lines long : rt*, segregate 

 retina; y l , ganglion. 



44. A similaiv section from a more advanced larva. 



45. A similar section from an adult larva. 



46. The bacilla from the neuron of the same larva. 



47. The bacilla from the neuron of a Dragon-fly larva {Libelhda depressa). 



48. The cephalic ganglia of a Cockroach, from a large larva, seen from behind : op, optic lobe ; 



n, nerves to partial retinae. 



49. The same, seen from before. 



50. A transverse section through one of the partial retime in a rudimentary stage : no, one of the 



optic uerves. 



51. A section through the neuron of a Fly (Syrphus ribesii). 



52. A portion of the retinal ganglion of the same, seen with an immersion lens j^. (The references 

 as in fig. 42.) 



53. Two bundles of bacilla from the retina of the Blow-fly, from an osmic-acid preparation, showing 



the tracheal vessels and cells of the neuroglia : o outer and i inner segments. 



54. A transverse section through the entire eye of a Gnat. 



55. Bacilla from the eye of Tipula, showing the axis-cylinder between the inner and the outer 



segments. 



Plate XLIII. 



Fig. 56. A semidiagrammatic representation of the retina of the Blow-fly, drawn from preparations 

 prepared in different fluids, and showing the connexions of the various elements : a, neuroglia, 

 of the retina, from a chloral hydrate preparation ; b, the same, from an osmic-acid preparation ; 

 " c, the bacilla, from osmic-acid preparations ; B 1 , outer segments ; B 2 , inner segments ; d, the 

 neurogba of the optic nerve ; e, the fibres of the optic nerve, from osmic-acid preparation ; 

 /, outer layer of ganglion, osmic acid ; g, cells with the supporting neuroglia, chloral hydrate ; 

 h, transverse fibres, Midler's fluid; »r, inner limiting membrane of retina ; m 3 , endothelium 

 covering the ganglion ; no', inner nerve-fibres connecting the optic and deep ganglion. The 

 other references are the same as those in the rest of the figures. 

 57. A portion of the neuron of a Crane-fly {Tipula oleracea). The references as in fig. 56. 



