386 ZOOLOGY. 



vesicles, which perform the functions of a reservoir of air 

 (Fig. 48). The apertures by which the air penetrates into 

 the trachea are called stigmata; they resemble in general a 

 small button-hole, but these often have valves which open 

 and shut like the folding or clapper of a door. A pair may 

 generally be seen on the lateral and upper parts of each ring j 

 but they are often absent in the last two segments of the 

 thorax. 



With regard to the mechanism by which the air is renewed 

 in the interior of this respiratory apparatus, it would seem 

 to consist generally in the movements of contraction and 

 dilatation of the abdomen. Thus, as we have already said 

 elsewhere, the respiration is very active in these animals. 

 They consume a considerable quantity of air, compared with 

 their bulk, and speedily asphyxiate when deprived of oxygen ; 

 but when they are in this condition of apparent death, they 



I 



Fig. 366. Male Lampyris Fig. 367. Female Lampyris. 

 (Glow-worm). 



can continue so for a great length of time without losing the 

 faculty of returning to life. 



528. Most insects produce but very little heat; but 

 some of these animals disengage, under certain circumstances, 

 a sufficiency notably to raise their temperature. Bees offer 

 an exan.ple of this, especially when they are much agitated 

 in their hive; and it is to be observed, that the respiration 

 becomes then very active. 



529. Another and a more remarkable phenomenon, and 

 of which the cause is still unknown, is the production of 

 light observed in some insects. The lampyris or glou'-irorm 

 is an example of this, well known to all who frequent the 

 fields : the male (Fig. 366), which has wings, is but little 

 luminous ; the female (Fig. 367), which has no wings, and 

 which is often found during the warm nights f summer on 

 the thickets, spreads around a very lively phosphotteseenl 



