Packakd] mental powers OF IXSECTS. 357 



which there is a true brain or mass of ganglia lodged in the 

 skull or brain-box ; though it may be added that the spinal 

 cord is in a degree a nervous centre in itself. 



The large e3'es of insects are made up of a great number 

 of simple eyes, the optic fibres from each one of these simple 

 e^'cs (indicated externally by facets) uniting to form a com- 

 mon nerve connecting with the brain. How large may be 

 sometimes the number of simple eyes united to form this 

 composite eye is seen in a certain butterfly which has 17,355 

 of them. The eye of the dragon fly consists of 12,544, 

 while the eye of the common house fly has 4,000 fiicets, or 

 cornese. In these insects the composite eyes are exceed- 

 ingly large, sometimes, as in the house fly or dragon fl}", 

 forming the greater part of the bulk of the head, Tliere is 

 every reason, from the complicated structure of the eye., 

 which we will not here describe, and from the movements of 

 these insects, to infer that they have acute powers of sight. 

 Even certain low insects and the young of the higher ones, 

 in which the eyes are rudimentary and single, have, it is 

 known from experiment, the power of distinguishing light 

 from darkness, a matter of considerable importance to these 

 insects, which mostly move about at night. 



While the eyes in insects are invariably situated on the 

 head, this is not the case with a large number of little sense 

 organs which are found in the antennae and the palpi or 

 feelers, attached to the accessory jaws (maxillae) and the 

 under lip (labium). 



These minute organs consist of a little cavity, covered by 

 a membrane, which is supposed to act as a tympanum. In 

 connection with the cavity is a nerve which runs to a gang- 

 lion. "When there are a number of these microscopic sense 

 organs placed together, the nerves i)roceeding from them 

 unite to form a common fibre, as in the antennal nerve. 

 This sense apparatus is supi)osed to be usually auditory in 

 its function, as it is in some form or other almost invariably 



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