THE SIMPLE AND COMPOUND EYES OF INSECTS. 
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Fio-. 23. Transverse sections of the rhabdia. 
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a. Section throughout the outer extremity of a rhabdion. 
b and c. Through the middle of the rhabdion. 
Fig. 24. The ganglionic retina of the same insect. 
(For figs. 25, 26, and 28, see Plate 54.) 
Fig-. 27. The tetrasome of Acridium seen from the surface of the cornea. 
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Fig. 29. The tetrasome of Vanessa atalanta. 
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PLATE 54. 
Fig. 25. The chamber of the eye of the nymph of Acridium. 
Fig. 26. The same, from an imago of the same. 
Fig. 28. Two chambers from the eye of Vanessa atalanta. 
Fig. 30. Four chambers seen from the surface of the cornea. For the sake of clearness, 
all the parts are only represented in one of the segments. 
Fig. 31. The rhabdion of the same. 
Fig. 32. Transverse section through some of the facelli of the same eye. 
Fig. 33. The ganglionic retina. 
Fig. 34. Vertical section through one of the facelli of the same eye. 
Fig. 35. The chamber of the eye of Colias. 
Fig. 36. A vertical section of a portion of the eye of a Hawk Moth from the pupa. 
Fig. 36a. One of the cones of the same. 
Fig. 37. One of the cones of the compound eye of a Noctuid. 
Fig. 38. A vertical section of a portion of the eye of another species of Noctuid. 
Fig. 39. A similar portion of the eye of a third species of Noctuid. 
Fig. 40. A transverse section through the compound part of the rhabdion, from the 
same insect as the last preparation. 
Fig. 41. A transverse section through sheaths of the rhabdia of a Noctuid Moth. 
Fig. 42. The cones seen from the cornea, from the same specimen as fig. 38. 
Fig. 43. An outline of the eye of Vespa to show the direction in which the principal 
meridians were drawn. 
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