THE BAG-WORM. 259 



ward (Fig. 97 &), makes a dive under it, turns a complete somersault and lies on its 

 back, held down by the band (.Fig. 97 c). By a quick turning movement the larva 

 regains its feet, the band now extending across its neck (Fig. 97 d). It then adds to 

 the band at each end until the two ends meet, and they are then fastened together 

 so as to form a kind of narrow collar which encircles the neck of the worm. Far 

 from resting, it now busies itself by adding row after row to the anterior or lower 

 end of the collar, which thus rapidly grows in girth and is pushed, further and further 

 over the maker (Fig. 97 e). The inside of this bag is now carefully lined with an 

 additional layer of silk, and the larva now marches off, carrying the bag in an up- 

 right position (Fig. 96 g and Fig. 97/). When in motion or when feeding, the head 

 and thoracic segments protrude from the lower end of the bag, the rest of the body 

 being bent upward and held in this position by the bag. As the worms grow they 

 continue to increase the bags from the lower end and they gradually begin to use 



a 



d e f 



Fig. 97. — Thyridopteryx ephemercBformis. How the young larva prepares its bag. After Riley 



larger pieces of leaves, or bits of twigs, or any other small objects for ornamenting 

 the outside. Thus the bags will differ according to the different kind of tree or shrub 

 upon which the larva happens to feed ; those found on coniferous trees being orna- 

 mented with the filiform pine leaves, usually arranged lengthwise on the bag, while 

 those on the various deciduous trees are more or less densely and irregularly covered 

 with bits of leaves interspersed with 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. When the bags, with the growth of the larva, get large and heavy, they are 

 no longer carried, but allowed to hang down (Fig. 96/). The worms undergo 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 recovered, from this eff'ort. 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 the thoracic joints are horny and 

 mottled with dark-brown and white (Fig. 96 a). The numerous hooks with which 

 the small, fleshy prologs 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. 96/) is elongate-oval in shape, its outlines 

 being more or less irregular on account of the irregularities in the ornamentation 



