38 FIELD ZOOLOGY. 



to take care of itself, provide for itself, and look after the 

 wise placing of its eggs in the future, if it is a female moth. 

 The internal changes are also great. The musculation of 

 the caterpillar is that of a worm, for crawling, wriggling, 

 worm-like locomotion, and instead of long muscles we 

 find many short muscles running lengthwise of the body, 

 while other muscles run around the body at nearly right 

 angles with these. In the adult the muscular needs are 

 very different, where, especially in the thorax and the head, 

 many strong cross muscles must provide for flying, run- 

 ning, and eating. The alimentary canal of the larva is 

 adapted for disposing of solid food, while in the adult 

 stage the alimentary canal is adapted for sucking liquid 

 food from flowers. 



Not only are there changes such as have just been 

 described for the butterflies and the moths, but the 

 respiratory systems of some insects must also change. 

 The dragon-fly nymphs are adapted for living in the water, 

 while the adult dragon flies are air-breathing insects. 

 The heart and the nervous system of an insect with 

 complete metamorphosis, show lesser differences, but 

 even here there must be changes on the way to adulthood. 

 The ventral nerve chain of the larvae of some insects con- 

 tains twice as many ganglia as does that of the adult; 

 the cephalic ganglion enlarges on the way toward the 

 mature insect, and the front part of the larval heart 

 gradually narrows at the head end into what may be 

 called, in some insects, the aorta. 



In the pupal stage the insect is defenseless; it can 

 neither fight nor run away; hence its safety lies in con- 

 cealment in some burrow, or in the sagacity with which 

 its larva spun a cocoon and hung itself up where it would 

 not show, or where it would so harmonize with its sur- 



