380 w. wesche ox the structure of the eye-surface 



The conclusion I arrived at was that pubescence has but little 

 to do with the sight. I then considered that it might be 

 protective, and certainly in the case of Bibio it may well be so r 

 as the flight of the male is often exceedingly quick and head- 

 long, and the curious sexual fury that finds vent in dances and 

 other antics may cause him to blunder up against hard objects 

 and suffer injury. The long pubescence in this genus would make 

 quite an elastic protective cushion. But there are a number of 

 factors to be taken into consideration ; as although we find it so- 

 highly developed in the male and so markedly contrasted by its 

 total absence in the female, it seems a character confined to that 

 family, and the much weaker sexual developments in the 

 Tabanidae and Hyetodesia may be vestigial. 



The character as a non-sexual one is an archaic one, and its 

 presence in so many families in an equal state of development in 

 both sexes seems to point out that it has some advantages, 

 though this idea is difficult to reconcile with its absence in Bibio ? , 

 and its weaker character in the same sex in Hyetodesia. 



On the whole, I think it is in some cases protective in the 

 male ; that the females of Haematopota and Hyetodesia have 

 partially developed a character of the opposite sex; and in the 

 remaining cases, where it is equally developed in both sexes, that 

 the females have wholly developed the male character, and it 

 has ceased to be sexual. An analogous case to this has occurred 

 in the Cyrtidae in the matter of the size of the eyes. 



The Chitinous Structure of the Eyes. 



Two cards placed a millimetre apart were pierced in a similar 

 manner to the other cards, so that the rays of light would pass 

 through a dark chamber of greater depth than in the former 

 experiments ; a bright light was focused on a card, and the 

 dots of light seemed sharper and more exactly defined than in 

 the previous experiments. 



Some arthropods of very archaic type, such as Scolopendra,. 

 have only simple eyes, circular apertures pierced in plates of 



