170 NATURAL HISTORY. 



more rapidly than at others, and in this way even raise the temperature 

 of the hives several degrees. The exertion apparently affects these insects, 

 and it is stated that it actually produces a perspiration. 



We have said that these air-tubes permeate all parts of the body ; but 

 no one except those who have studied the microscopic structure of insects 

 can know what this means. The larger tubes are readily seen and fol- 

 lowed by ordinary dissection ; but they soon break up into smaller branches, 

 which cannot so readily be seen. When we turn to the microscope for 

 farther aid, we find that these minute branches still farther divide, and 

 penetrate even to the interior of the eye, into the tissues of the viscera, and 

 into the legs and wings. 



Most wonderful of all are the metamorphoses which many insects 

 undergo. It has been used by poets to furnish many a figure, while the 

 theologian calls upon it for analogies to support some of his articles of 

 faith. These changes have often been described, but no one has yet 

 exhausted the subject. Each year as spring returns, beetle and butterfly 

 emerge from the chrysalis to follow their short life as perfect forms, and 

 then to die ; but only after they have left behind them the eggs, which 

 after they are gone are to go through the same wonderful changes. 



These changes are most familiar in the group of butterflies, and hence 

 we will briefly describe them there. The butterfly which flits about from 

 flower to flower in a seemingly aimless way has really important business 

 on hand. She has a stock of eggs to dispose of, and these she must deposit 

 in a proper place. Keep her in confinement, and she will lay them in the 

 box in which she is kept ; but leave her to herself, and she will seek out the 

 plant which will afford the best food for the young larvae soon to hatch 

 from them. 



Many of these eggs seen under the microscope are objects of extreme 

 beauty ; some are colored the most delicate colors, others are ornamented 

 with ridges, or spines, or both, sometimes arranged in the most complex yet 

 symmetrical patterns. These eggs are laid either singly, or in large masses, 

 or again each egg may be supported on the tip of a long and slender pedicel ; 

 in short, there is no end to the variety of insect eggs. From the egg 

 hatches out the larva, — a long, slender, worm-like body, sometimes smooth 

 and naked, at others clothed with various spines and hairs. In almost every 

 instance the larva is protected to a certain extent from its ordinary ene- 

 mies. Its colors may be such that it is not readily distinguished on the 

 plant on which it feeds ; or again, its fur or spines render it an object 

 which does not please the mouth or palate of insect-feeding birds. Still 

 others are provided with scent-glands which secrete a strong, frequently 

 an exceedingly nauseous, odor. All these are protective. Still other larvse 



