362 INSECTA. 



distinguished from the larva by a considerable increase of vigour and 

 energy in its movements. In the imago the concentration of the nervous 

 centres is carried to that extent which is adapted to the necessities of 

 the mature state : their number is still further reduced (fig. 182, c) ; 

 their size, in the thorax especially, considerably increased ; and the 

 brain, now arrived at its maximum of development, is furnished with 

 the wonderful apparatus of eyes, and other instruments of the senses, 

 which heretofore would have been absolutely useless, but now, with the 

 expansion of the brain, have become suited to the more exalted faculties 

 of the insect. 



(932.) Many insects are capable of producing audible sounds ; and 

 sometimes the noises they make are exceedingly shrill, and may be 

 heard at some distance. Such sounds originate from various causes in 

 different tribes, and it is not always easy to detect the mode of their 

 production. In many Beetles they are caused by rubbing different 

 parts of their dense integument against each other ; and the chirping of 

 several OrtJioptera seems to have a similar origin : the acute note that 

 these insects utter is apparently produced by friction, the edges of their 

 hard pergamentaceous wings being either scraped against each other, 

 or against the long and serrated edges of their thighs. The buzzing 

 and humming noises heard during the flight of many genera result from 

 the forcible expulsion of the air as it streams through the respiratory 

 spiracles, whose orifices Burmeister imagines are furnished with vibratory 

 lamina?, to the rapid movements of which the noise may be due. In the 

 genera Gryllus and Cicada among the Orthoptera, 

 however, there is a peculiar apparatus specially Fi &- 183- 



provided for the production of the loud chirping to 

 which such insects give utterance. Upon the first 

 segment of the abdomen, covered by a broad move- 

 able plate (fig. 183, a), there is a large aperture, 

 wherein a tense plicated membrane is observable. 

 This membrane is acted upon internally by cer- 

 tain muscles able to throw it into rapid vibration, 

 and thus give rise to the sound in question. 



(933.) One other point connected with this 

 interesting class of animals requires brief notice. 

 Many insects are endowed with the faculty of 

 emitting phosphorescent light, which is in some 

 species exceedingly brilliant. The Elateridce Musical apparatus of a- 



-n , , ., . ., cada : a, moveable horny 



among Beetles are pre-eminently luminous ; and p i a te, drawn aside to display 



in them the light seems to be principally given the P 11 ** * membrane; &, 



* e rings of the abdomen. 



out by two oval spaces upon the thorax, which 



in the dead insect are of a greenish hue : during life, some species 

 (Elater noctilucus) are so strongly phosphorescent as to enable a person to 

 read a book by passing the animal over the lines. The Lampy rides emit 



