SIE JOB^N LUBBOCK ON AT^TS, BEES, ATSD WASPS. 



125 



On the Function of the Compound Etes and Ocelli. 



Eorel agrees with Reaumur, Marcel de Serres, and Duges, that 

 in insects which possess both ocelli and compound eyes the 

 ocelli may be covered over without materially affecting the move- 

 ments of the animals ; while, on the contrary, i£ the compound 

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

 Eorel varnished over the compound eyes of some flies {Calli- 

 phoria vomitoria and Liicilia casar), 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 repeatedly 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. 

 Einally, they ended in flying away straight up into the air and 

 quite out of sight. 



Johannes Miiller inclined to the opinion that insects saw near 

 objects with their ocelli. Plateau satisfied himself that the move- 

 ments of insects are not affected by the ocelli being covered over, 

 and hence concluded that they are rudimentary organs. The com- 

 plexity of their structure, however, seems fatal to tliis conclusion. 



Eorel confesses that the use of the ocelli still remains an 

 enigma, but he is disposed to think that tliey enable their 

 possessors to see in comparative darkness. He observes * that 

 they are specially developed in insects which require to see both 

 in bright light and also in comparative obscurity. Aerial insects 

 do not generally require or possess ocelli. 



Lebert expresses the opinion f that in spiders some o£ their 

 eight eyes — those which are most convex and brightly coloured — 

 serve to see during daylight ; the others, flatter and colourless, 

 during the dusk. Pavesi has observed % that, while the species 

 of Nesticus possess normally eight eyes, in a cave-dwelling species 

 {NesticMS speluncarum) there are four only, the four middle eyes 

 being atrophied. This suggests that the four central eyes serve 

 specially in daylight. 



Sknse of Smell. 



In ray previous memoirs I have recorded a few experiments 

 which convinced me that ants are gifted with a very highly 

 developed sense of smell, and that this resides in the antennae. 



* i. c. p, 181. t Die Spinnen der Schweiz, p. 6. 



\ " Sopra una nuova specie di Eagni appartenente alle coUeziuni del Museo 

 Civico di Geiiova," Ann, Mus. Civ. 1873, p. o44. 



