222 THE INSECT WORLD. 



glands. At this period the animal eats much ; and it is certain that 

 the substance to be converted is furnished by the leaf of the tree on 

 which the insect feeds. 



In consequence of this having been remarked, some manufacturers 

 have attempted to obtain their silk directly from the mulberry leaf; 

 but they only get a bad floss or refuse silk. This is because the silk 

 is not formed in the mulberry leaf. The organs of insects are labora- 

 tories, in which manipulations unknown to man are carried on, 

 manipulations which he has not been able to imitate. 



After this rapid glance at the fundamental parts of the organism 

 of the silkworm, we will occupy ourselves with the natural history, 

 properly so called, of this insect, and with its rearing, carried on with 

 a view to the production of silk. 



As belonging to the first part of this programme, we have to speak 

 of the moult, of the ages of the silkworm, of its maturity, of its 





Fig. 202. Fig. 203. 



Head of the Silkworm during moulting. Position of Silkworm while moulting. 



mounting or ascending season, of the formation of the cocoon, of the 

 chrysalis, of the moth, and the eggs. 



The name moult has been given to a sort of crisis during which 

 the renewing of the skin of larvae takes place. When it approaches, 

 the silkworm changes its colour. Its robe, which was white or grey, 

 and opaque, becomes yellow and somewhat transparent. The head 

 swells considerably, especially above, and the skin becomes wrinkled 

 (Fig. 202). The worm then fasts, and prepares to cast its skin. It 

 places here and there some silk threads on the surrounding objects. 

 It then slips under these threads, so that during its movements the 

 old skin which it will abandon is, so to speak, gathered up. It then 

 assumes a peculiar position, that represented in Fig. 203, and remains 

 in it in a state of immobility which has been called sleep (sommeU). 



During this sleep the new skin is formed under the old. A liquid 

 oozes forth between the two membranes which separates them, and 

 allows the silkworm to leave its old skin. To effect this, the worm 

 begins by raising its head, and by making contortions. The old skin 

 splits round the muzzle, or snout, on the head and back ; then by 



