— 35 — 



Carriere, on tlie other liajid, comes to regard the pseudo- 

 cone as part of the cornea. In recent times Dietrich also 

 joined to this point of vieAV. He was lead to this conchision 

 by observing that in some species, e. g., Simulium and Chry- 

 sogaster, there is no sharp demarcation between the facet and 

 pseudocone, as the folds of the former pass uninterrupted 

 into the latter. 



I did not succeed in noticing any connection between the 

 pseudocone and cornea in my preparations. The cornea 

 usually became separated from the pceudocone without car- 

 rying along with it any pieces of the latter, the shrivelled 

 remnants of the pseudocone always remaining witli the crys- 

 talline cells. But, although my observations do not agree 

 with D i e t r i c h's views on the origin of the pseudocone, 

 I have no serious objections which I could put against this 

 view. 



The Retinulae (Retina). 



The retinulae (fig. 3 and 9, ret) form the sensory apparatus 

 of the facetted eye. In Diptera each retinula has the cha- 

 racter of a tube lying proximally to the crystalline cells. The 

 walls of the tube are composed of 7 rhabdom cells which are 

 elongated and are adjacent with their edges. On the interior 

 side each of these cells bears a sensory rod, or rhabdomere 

 (fig. 9 and 12, rh), which protrudes into the central lumen of 

 the retinula. In the proximal direction the retinulae are 

 underlaid by the basilar membrane (bm). 



In all parts of the eye the retinulae are built nearly alike, 

 exceptmg its anterior surface where they differ somewhat from 

 the general type. For comparison I am giving three figures 

 is, 4 and 5). In fig. 3 the longitudinal section did not pass 

 through the anterior portion of the eye, on account of that all 

 the retinulae are about the same there, and only on the edge 

 of the middle area they are somewhat larger, as it is usual 

 in the facetted eye. The anterior part of the eye is represented 

 in transverse section in fig. 5, and in longitudinal — in fig. 4. 

 In the transverse section it is seen that the retinulae of the 

 anterior surface of the eye (a) are nearly twice longer than 

 the retinulae of its other parts (d, v and p), on account of 



