400 Dr. Sharp's account of recent experiments 



Lepidoptera — that have been made blind, either by 

 covering the whole of the eyes with black pigment, or by 

 severing the nervous cords, and that are afterwards 

 released in the open air, rise vertically in the atmosphere 

 to a great elevation. 



2. When the function of the compound eyes is de- 

 stroyed, the ocelli remaining intact, insects (Hyme- 

 noptera, Odonata, Diptera) behave exactly in the same 

 manner as they do when the ocelli are likewise destroyed. 

 That is to say, when liberated in the open air, they rise 

 upwards vertically, and when flying in a room lighted by 

 windows situated on one side only, they also present the 

 same peculiarities as are seen in individuals all of whose 

 eyes have been either covered over or incised. 



3. If the function of the ocelli be alone destroyed, the 

 compound eyes remaining intact, diurnal winged insects 

 are apparently not aware that they have been deprived 

 of any organ of sensation, and to all appearance behave 

 exactly like insects in their natural state. 



4. In diurnal insects furnished with compound eyes, 

 the simple eyes are of almost no use, and in every case 

 only afford to their possessors feeble sensations of which 

 they are unable to make use.* 



The results that we may consider as plausible hypo- 

 theses supported by a certain number of previously 

 ascertained facts are : — 



1°. Diurnal insects, in which the effectiveness of all 

 the eyes has been destroyed, still possess dermatoptic 

 perceptions : 



2°. They must be pretty nearly reduced to the use of 

 these latter perceptions when their frontal ocelli still 

 remain to them : 



3°. Dermatoptic perception must be the chief cause of 

 the ascending flight of blinded insects liberated in the 

 open air : 



4°. The ocelli cannot be of use either for perceiving 

 movements of neighbouring objects, nor for distinguishing 

 light in comparatively gloomy conditions. 



* This conclusion is only correct so far as Tocomotion is con- 

 cerned, no experiments having been made with a view of testing 

 to what extent the ocelli may be useful in industrial occupations, 

 or actions other than those of locomotion. — D. S. 



