LEPIDOPTERA. 



221 



of the intestinal canal and below it. This is the apparatus which 

 secretes the silk; it is the double silk-bearing gland. Each one of 

 these glands is composed of a tube formed of three distinct parts 

 (Fig. 201). The part which is nearest to the tail of the worm is a 

 bent tube, a b c, of a thirtieth of an inch in 

 diameter, and about nine inches in length, twisted 

 a great many times into irregular zigzags. This 

 ; part of the silk-producing organ is continued in an 

 enlarged portion, d e, which is the reservoir of 

 the silky matter. To the extremity, e, of this 

 reservoir, is attached another capillary tube, e f. 

 These two capillary tubes, proceeding from the 

 two glands, unite together like two venous trunks, 

 .as the plate shows, in one single, short canal, f, 

 .which opens in the mouth of the worm, at its 

 under-lip. 



It is in the narrow hinder tubes that the silky 

 matter is formed. It collects in the swollen part 

 D E, which is, properly speaking, the reservoir; 

 and remains there in the glutinous state. Having 

 reached the capillary tubes, it begins to assume 

 consistency, and forms ^two threads, which are 

 .united together at the point of junction of the 

 tubes, and come out through the orifice, with the 

 appearance of a single thread, to be conducted 

 and directed by the animal to those points it has 

 selected. 



It was hoped that by taking from the body siik secreting apparatus. 

 ,,Qf the worm the vi'scous matter contained in the 

 iglands, silk could be formed. But this hope was disappointed. It 

 ;Was found possible, it is true, to take the silk out ; to draw it out 

 jinto threads more or less fine ; but up to this time it has only been 

 fl possible in this way to obtain a matter which, when dried, more or 

 less resembles catgut, and is easily enough spoilt by water. 



The viscous substance contained in the glands must then be 

 .elaborated by the insect itself. When it arrives in the conduit 

 common to the capillary tubes, under the form of a thread, it is 

 impregnated with a sort of varnish, which is poured into them from 

 two neighbouring glands. The varnish unites the two threads into 

 ^,one single thread, and imparts to it the brilliancy of silk, and the pro- 

 ;Perty of resisting the action of water. It is during the last phases of the 

 worm's development that the silky matter becomes abundant in the 



