ON FUNCTION OF COMPOUND EYES AND OCELLI. 407 



the ultra,-violet rays with their eyes ; and not, as 

 suggested by Graber, by the skin generally. 



Experiments with Platyarthrua, 



In connection with this subject I may add that I do 

 not at all doubt the sensitiveness to light of eyeless 

 animals. In experimenting on this subject I have 

 always found that though the Platyarthrus, which live 

 with the ants, have no eyes, yet if part of the nest be 

 uncovered and part kept dark, they soon find their 

 way mto the shaded part. It is, however, easy to 

 imagine that in unpigmented animals, whose skins are 

 more or less semi-transparent, the light might act 

 directly on the nervous system, even though it could 

 not produce anything which could be called vision. 



On the Function of the Compound Eyes and Ocelli. 



Forel agrees with Reaumur, Marcel de Serres, and 

 Dug^s, that in insects which possess both ocelli and 

 compound eyes the ocelli may be covered over without 

 materially affecting the movements of the animals ; 

 while, on the contrary, if the compound eyes are so 

 treated, they behave just as in the dark. For instance, 

 Forel varnished over the compound eyes of some flies 

 {Galliphora voinitoi'ia and Lucilia ccesar\ and found 

 that if placed on the ground they made no attempt to 

 rise, while if thrown in the air they flew first in one 

 direction and then in another, striking against any 

 object that came in their way, and being apparently 

 quite unable to guide themselves. They flew re- 

 peatedly against a wall, falling to the ground, and 

 unable to alight against it, as they do so cleverly when 

 they have their eyes to guide them. Finally, they 

 ended in flying away straight up into the air and quite 

 out of sight. 



Johannes Miiller inclined to the opinion that in- 



