INSECTS IN COMMERCE 137 



head, this soaks through the silk and disunites 

 the threads, so that the moth is able to push 

 it head through them, and emerge without 

 breaking the silk. 



The way in which the silk is formed is 

 exceedingly interesting. Down each side of 

 nearly the entire length of the silkworm's body 

 runs a silk-producing gland ; at the tail end of 

 the insect these glands consist of fine tubes about 

 the thirteenth of an inch in diameter, bent and 

 twisted into a number of zigzags, which, when 

 straightened out measure nine inches in length. 

 Within these slender tubes the silky matter is 

 formed ; it then passes on into the central portion 

 of.the glands, which are much enlarged, forming a 

 kind of reservoir; here the silk, which is then of 

 a glutinous consistency, is stored. The glands 

 then again become narrowed into two capillary 

 tubes, which finally unite and become joined in 

 a single, short canal opening into the mouth of 

 the insect. As the silky substance passes from 

 the reservoir down these tubes it gathers con- 

 sistency, and forms two threads which unite at 

 the juncture of the glands and pass out of the 

 mouth of the silkworm as a single thread. As 

 the thread passes down the final conducting tube 

 it becomes imbued with a secretion poured upon 

 it from two neighbouring glands, which acts upon 

 it as a kind of varnish, giving the silk its brilliancy 

 and water-resisting qualities. 



During the latter period of the larval state 

 (while the silk is rapidly forming) the silk- 

 worm's appetite is simply enormous; and it has 

 been calculated that thirty grammes of eggs will 



