— 33 — 



The length of the stalks varies also in the limits of one 

 species especially in different sexes, the male possessing so- 

 mewhat longer stalks than the female. On account of this, 

 the authors formerly used to base their determination of the 

 sex in doubtful cases on the length of the stalks. At the dis- 

 tal end, on which the eye sits, each stalk thickens conside- 

 rably, in this thickening the optic ganglion is situated. 



The facetted eye (fig. 1 — dorsal view, fig. 2 — ventral 

 view) in the species investigated by me is very uniformly 

 organized. It has the same structure in both sexes, and exhi- 

 bits no other external differentiation into a double eye, except 

 an increase of facets in the anterior part of the eye. 



The shape of the eye is very irregular, nearly oviform. 

 The distal external surface of the eye („Augenmittelfeld") is 

 the most convex. The stalk is attached to the eye from behind 

 and by the dorsal side, so that the largest free surface of 

 the eye is situated on its anterior and lower part. The degree 

 of development of the facets partly corresponds to this orienta- 

 tion of the eye: the largest facets are situated on the anterior 

 surface of the eye, whereas the remaining parts of the eye, 

 and especially the posterior possess facets of a much smaller 

 size. 



Anteriorly to the bases of the eyes are attached the three- 

 jointed antennae with a large, flat terminal joint, carrying a 

 long, thin terminal seta. Beginning from the base of 

 the antennae, the anterior side of the eye-stalk under which 

 the optic nerve passes is slightly raised. The dorsal border 

 of this prominence usually passes as a thin line along the 

 stalk (fig. A), and is continued on the head into the so-called 

 linea arcuata; the latter bears the character of a vide, mostly 

 black line, dividing the forehead from the face. On the fore- 

 head there are three ocelli situated dorsally (fig. A, oc). 



The Cornea. 



The cornea presents the cuticle of the eye, which became 

 defferentiated into hexagonal facets in such a way that one 

 facet corresponds to each ommatidium. Towards the exterior 

 the facets are convex and rounded, as it may be seen from 

 fig. 10, on the right side of which the section has passed 

 through the surface of the facets. In longitudinal section 



