THE SILKWORM ITS FORM AND LIFE HISTORY. 23 



upwards of a week's incessant feeding, during which it has eaten 

 more than in all the rest of its life put together, and has acquired 

 a length of three inches or upwards, it begins to change colour, 

 turning yellowish, and putting on a waxy appearance, the skin 

 becoming almost transparent. It nibbles its food and scatters 

 the fragments about without attempting to eat them ; it appears 

 restless and begins to wander from the well-supplied pastures it 

 has never before shown any inclination to leave. It moves its 

 head about in all directions apparently feeling for something, 

 which its instinct suggests to it, ought to be near at hand. It 

 begins to climb every obstacle it encounters, being especially 

 anxious to work its way "upward." It disdains its old litter, and 

 " Excelsior " is its watchword. At the same time it is continually 

 producing silk from its spinneret and attaching threads of it to all 

 objects around. All these signs indicate that the spinning time is 

 at hand. The caterpillar is now desirous to provide a retreat for 

 itself in which to perform the last two changes of its skin 

 moults, each of which will produce a far more startling and 

 remarkable alteration in its appearance than either of the preceding 

 has done. The first is the change to a chrysalis, the second, the 

 change to a moth. It has now to look forward to from three to 

 five days of incessant toil, while it abstracts from its own body 

 the material necessary to enshroud itself. 



It is not long in selecting a spot suitable for those momentous 

 epochs in its life, and at once begins to lay the foundations of 

 that beautiful cocoon, which is so highly valued by human kind. 

 Its first operation is to run threads of silk backwards and forwards 

 in an irregular way, from one support to another, at the extreme 

 limits of the space it has decided to occupy, and to continue them 

 farther and farther inwards till only a small oval space is left in 

 the centre, not more than an inch and a quarter long, in which it 

 can only just turn round. Thus far it has not commenced the 

 cocoon proper, these threads being only the outworks, as it were, 

 of its snug fortress, intended to support it and fix it securely, 

 and the actual form and arrangement of the mass will depend 

 entirely upon the exigencies of the position selected. When this 

 " floss," or " refuse silk," as it is called, is finished which will be the 

 case after some five or six hours, the caterpillar devotes its atten- 

 tion exclusively to the oval space it has thus enclosed, and begins 

 with much more care to run a continuous thread backwards and 

 forwards upon the walls of this till a very compact, tough and 

 perfectly opaque, hollow, oval structure is formed (Fig. 9), in the 

 centre of which the caterpillar remains bent almost double, or 

 twisted in the form of an S, so cramped is it for room. This is 



