LESSON 92.] THE EYE IN INSECTS. 297 



ment, has compound eyes of unusual size, and which offer great facil- 

 ities for studying the structure of the transparent cornea, and espe- 

 cially of the lenses. 



1343. It has been already remarked that the cornea is lined with 

 a membrane, to the posterior portion of which the crystalline lenses 

 are attached, and removing this from the cornea of Prionus, and sub- 

 mitting it to the microscope, an interesting scene presents itself. 



1344. The lines which separate the corneas severally, are strongly 

 marked ; the cells are, generally, perfectly round, although those to- 

 wards the margins are oval, and quite flat; these cells are so many 

 open holes (Fig. 423), as if to admit the anterior portion of the true 

 crystalline lens ; moreover, being smaller, they act as stops to a struc- 

 ture yet to be described. 



1345. If we now examine the cornea from which this membrane 

 has been detached, a very remarkable sight meets us. 



1346. The cells, or the transparent spaces of the cornea, are fill- 

 ed with a series of crystalline prisms, Fre 



which stand up far above the level of 

 the membrane in which they are situ- 

 ated ; some of them are round, others 



Fro. 423. 



Posterior layer of the transparent Prismatic lenses in situ, Prionus Ion- 



cornea, P. longimanus. gimanus. 



oval; hexagons (six sides), pentagons (five sides), cubes, and even 

 triangles, are all represented in one or other of these prisms (Fig. 

 424). They appear to be so firmly impacted in the cells, that it is 

 only reasonable to suppose that they fit it accurately ; in this case 

 the anterior portion must be convex, fitting the concave inner surface 

 of the cornea. The terminal portions now presented to the specta- 

 tor, and which were applied to the round holes of the membrane 

 removed, are perfectly flat, but much larger than the round holes, 

 which, as before remarked, act as stops. This would give a series 

 of plano-convex lenticular bodies, sealed up, as it were, in the sub- 



