2 4 



SILKWORMS. 



the true cocoon or, as it is commercially termed, the " pod," the 

 part which is used for obtaining the best silk, and all that man 

 has to do is simply to unwind that long thread which the cater- 

 pillar is here twisting and winding about in all directions as fast 

 as it is produced. 



The silk is formed inside the body of the silkworm, as a kind 

 of gum which hardens on exposure to the air. When the little 

 labourer wishes to commence spinning, a drop of this gummy 

 substance oozes from the perforation in the spinneret, which is 

 then pressed upon the spot from which the thread is to start. It 

 instantly adheres, and then the caterpillar, moving its head away, 

 draws the gummy secretion out in the form of an exceedingly 

 fine thread, till the next point of attachment is reached, and the 

 thread caused to adhere as before, and so the process goes on till 

 the requisite amount has been produced. In forming the compact 

 portion of the cocoon, the silkworm does not wind the thread 





- : ; 

 c ' r 



Fig. 9. " Pod'' of Silkworm cocoon. 



Fig. 10. Strangulated cocoon. 



round and round, as might be supposed, but, placing itself with 

 its legs outwards, and then bending its head over its back till it is 

 almost double, it sways its head backwards and forwards, con- 

 tinuously tracing a series of figures of eight, the coils being laid 

 across one another, and adhering together by reason of the natural 

 stickiness of the thread. When it has laid a considerable length 

 in one spot, the indefatigable worker . shifts its position, and per- 

 forms the same operation in another, and so on, without ceasing 

 its toil, or breaking its thread, till the whole cocoon is finished. 

 From this it will be seen that the cocoon is composed of a series 

 of patches, as it were, all stuck firmly together, and consisting of 

 one continuous thread, but each patch, nevertheless, formed of an 

 overlying series of loops in the shape of a double curve. 



The length of thread thus produced depends upon the size and 

 vigour of the insect, and upon the amount and nature of the food 

 it has eaten. In the best breeds when most carefully reared an 

 enormous length is formed, ranging from seven hundred to one 

 thousand three hundred yards ; in other words, the thread of a 



