526 THI-. .s7-:.YN/:\V A.\D SEKSORY ORGANS. 



5. THE COMPOUND EYE OF THE BLOW-FLY. 



a. The Structure of the Dioptron. 



The dioptron consists of the cornea, the basilar membrane, 

 and the scleral ring, which form its case, and of the ommatea 

 or radially arranged eyelets. Each ornmateum corresponds to 

 a corneal facet, and there are between 4,000 and 5,000 facets 

 in each eye. 



The Cornea. I have already shown elsewhere [233] that 

 there are several verv distinct forms of cornea in the Arthro- 



<J 



poda. These I named the continuous cornea, the faceted 

 cornea, the kistoid cornea, and the lenticular cornea. 



The cornea of the Blow-fly is a kistoid cornea. That is, it 

 consists of a thin cuticular lamina with concavo-convex facets, 

 each facet strengthened and supported by a hexagonal frame 

 which separates the adjacent lenses frojn each other. 



Thus the cuticular lamina of the cornea exhibits very 

 shallow hexagonal alveoli with concave ends when viewed 

 from its inner surface. These alveoli are filled up by bi-convex 

 lenses. 



The substance of the lenses stains readily in mature pupae, 

 is highly refractive during life and shortly after death, but soon 

 loses its refringent power. In dried specimens, each lens is 

 seen split into four segments, and the same result is brought 

 about by treating a fresh cornea with ether. These segments 

 drop out in sections and leave only the cuticular alveoli. 

 In well -preserved specimens the lenses remain //; situ and 

 exhibit no apparent structure. In specimens preserved with 

 osmium peroxide the lens is well seen, it is stained a pale 

 brown, and is strongly bi-convex, without, so far as I can see, a 

 trace of apparent structure. In pup.-e about eiglit days old the 

 lens is represented by four nucleated cells. 



In the Cockroach (lUdttd) and the Earwig (Forficula} the 

 conn a is kistoid, and I have frequently separated the lenses ; 

 this I have been unable to accomplish in the Blow-fly. The 

 lenses so separated may be ruptured by pressure, and then 



