88 THE bbb-kbepbe's guidb ; 



vitalizing oxygen into every part of the insect org'anistn. As 

 shown long ago by Leydig and Weismann, these air-tubes are 

 but an invagination of the derm of the insect. What is more 

 curious, these tracheae are molted or shed with the skin of the 

 larvse. In the more active insects — as in bees — the main 

 trachea, one on each side of the abdomen, are expanded into 

 large air-sacs (Fig. l,y). Insects often show a respiratory 

 motion, which in bees is often very marked. Newport has 

 shown that in bees the rapidity of the respiration, which varies 

 from twenty to sixty per minute, gauges the heat in the hive, 

 and thus we see why bees in times of severe cold, which they 

 essay to keep at bay by forced respiration, consume much 

 food, exhale much foul air and moisture, and are liable to 

 disease. Newport found that in cases of severe cold there 

 would be quite a rise of mercury in a thermometer which he 

 suspended in the hive amidst the cluster. 



In the larval state, many insects breathe by fringe-like 

 gills. The larval mosquito has gills in the form of hairy tufts, 

 ■while in the larval dragon-fly the gills are inside the rectum, 

 or last part of the intestine. The insect, by a muscular effort, 

 draws the water slowly in at the anus, where it bathes these 

 singularly placed branchiae, and then makes it serve a further 

 turn by forcibly expelling it, when the insect is sent darting 

 ahead. Thus, this curious apparatus not only furnishes 

 oxygen, but also aids in locomotion. In the pup^ of insects 

 there is little or no motion, yet important organic changes are 

 taking place — the worm-like, ignoble, creeping, often repulsive, 

 larva, is soon to appear as the airy, beautiful, active, almost 

 ethereal imago. So oxygen, the most essential — the sine qua 

 non — of all animal food is still needed. The bees are too wise 

 to seal the brood-cell with impervious wax, but rather add the 

 porous capping, made of -wax from old comb and pollen. The 

 pupse, no less than the larvas of some two-winged flies which 

 live in water, have long tubes which reach far out for the 

 vivifying air, and are thus called rat-tailed. Even the pupje 

 of the mosquito, awaiting in its liquid home the glad time 

 when it shall unfold its tiny wings and pipe its war-note, has 

 a similar arrangement to secure the gaseous pabulum. 



The digestive apparatus of insects is very interesting, and, 



