THE BAG-WORM. 25 



pieces of twigs. When kept in captivity the worms are very fond of 

 using bits of cork, straw, or paper, if such are offered to them. Wheo 

 the bags, with the growth of the larva, get large and heavy, they are no 

 longer carried, but allowed to hang down (Fig. If). The worms un 

 dergo four molts, and at each of these periods they close up the mouth 

 of their bags to remain within until they have cast their skin and re- 

 covered from this effort. The old skin, as well as the excrement, is 

 pushed out through a passage which is kept open by the worms at the 

 extremity of the bag. 



The young larva is of a nearly uniform brown color, but when more 

 full-grown that portion of the body which is covered by the bag is soft, 

 of light-brown color and reddish on the sides, while the head and tho- 

 racic joints are horny and mottled with dark-brown and white (Fig. la). 

 The numerous hooks with which the small, fleshy prolegs on the middle 

 and posterior part of the body are furnished, enable the worm to firmly 

 cling to the silken lining of the bag, so that it can with difficulty be 

 pulled out. 



The bag of the full-grown worm (Fig. If) is elongate-oval in shape, 

 its outlines being more or less irregular on account of the irregularities 

 in the ornamentation above described. The silk itself is extremely 

 tough and with difficulty pulled asunder. 



The larva 1 are poor travelers during growth, and though, when in 

 great numbers, they must often wander from one branch to another, 

 they rarely leave the tree upon which they were born unless compelled 

 to do so by hunger through the defoliation of the tree. When full- 

 grown, however, they develop a greater activity, especially when very 

 numerous, and, letting themselves down by a fine silken thread, travel 

 fast enough across sidewalks or streets and often for a considerable 

 distance until they reach another tree, which they ascend. This mi- 

 gratoiy desire is instinctive; for should the worms remain on the same 

 tree they would become so numerous as to necessarily perish for want 

 of food. 



Pupation. — The bags of the worms which are to produce male moths 

 attain rather more than an inch in length, while those which produce 

 females attain nearly double this size. When ready to transform, the 

 larva firmly secures the anterior end of the bags to a twig or branch, 

 and instinct leads it to reject for this purpose any deciduous leaf or 

 leaf-stem with which it would be blown down by the winds. The inside 

 of the bag is then strengthened with an additional lining ol' silk, and 

 the change to chrysalis is made with their heads always downward. 

 The chrysalis is of a dark-brown color, that of the male | Fig. 7 b) being- 

 only half the size of that of the female Fig. 7 e and Fig. 9 



The Imago or perfect Insect — After a lapse of about three weeks from 

 pupation a still greater difference between the two sexes becomes ap- 

 parent. The male chrysalis works its way to the lower end of the bag 

 and half way out of the opening at the extremity. Then its skin bursts 



