INSECTA. 



305 



Fig. 139. 



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 results from the forcible expul- 

 sion of the air as it streams through the respiratory spiracles, whose 

 orifices Burmeister imagines are furnished with vibratory lami- 

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

 the genera Gri/llus and Cicada among the Orthoptera, however, 

 there is a peculiar apparatus specially 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 moveable 

 plate (fig. 139 ), there is a large aperture, wherein a tense plicated 

 membrane is observable. This membrane is acted upon internally 

 by certain muscles able to throw it into rapid vibration, and thus 

 give rise to the sound in question. 



(350.) 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 

 Elateridse among beetles are pre-eminently lu- 

 minous, and in them the light seems to be 

 principally given 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 phospho- 

 rescent as to enable a person to read a book 

 by passing the animal over the lines. The Lampyri emit a light 

 of great brilliancy ; and in Italy, during the summer nights, the 

 groves, illuminated by their incessant scintillations, exhibit a scene 

 equally strange and beautiful. Such insects appear to have a 

 power of obscuring or exhibiting their light at pleasure ; but the 

 nature of the luminous secretion, if such it be, upon which their 

 luminosity depends, has as yet escaped detection.* 



* An interesting account of this subject is to be found in the article LUMINOUSNESS, 

 ANIMAL, by Dr. Coldstream, in the Cyclopaedia of Anatomy and Physiology. 



