74 INJURIOUS AND USEFUL INSECTS 



cocoon, the thread is delivered at a greater rate than a foot 

 per minute, and the coagulation must therefore be very rapid. 



When the larva has done feeding it rests for a short time. 

 The body shortens, the skin of the neck becomes wrinkled, 

 and a long silken thread may usually be seen trailing from the 

 spinneret. Provision has been made long before by the silk- 

 worm breeders for the next event, which is the ascent of the 

 larvae to the places where they will form their cocoons. These 

 are arranged above the feeding-trays. In old days mulberry 

 branches were set up to receive the climbing larvae. Then it 

 was observed that any other twigs would do as well, for after 

 this the larvae feed no more. It was long the practice to leave 

 each silk-worm to choose its own retreat, but this plan had 

 serious inconveniences. They often begin to spin so near 

 together, that the spiral turns of the threads become crossed, 

 and then double cocoons are formed, which cannot be un- 

 wound. To render this difficult or impossible, special cells of 

 wood or paper have been devised, in which two silk-worms 

 cannot find room to spin. When the larva has established 

 itself in a dark recess, it begins to spin, first securing its body 

 by threads attached to different fixed points. At length the 

 head begins to revolve steadily round the body, which is first 

 veiled and then completely hidden. In three days the cocoon 

 of golden or silver threads is complete, and the larva rests from 

 its labours. The withdrawal of so much silk has materially 

 reduced the size of the body, and this facilitates the casting of 

 the last larval skin. The silk-glands shrivel and disappear. 

 If the cocoon is carefully examined, it will appear that the first 

 and last portions of the silk-thread differ from the intermediate 

 portion, which greatly exceeds them in length. The first spin- 

 ning forms loose flaky masses, which can only be utilised as 

 silk-waste; then comes the chief bulk of the fibre, which is 

 readily unwound ; last of all, and next to the body of the silk- 

 worm, is an inner, felted tissue, which gradually becomes too 

 close for unwinding. 



Ever since the beginning of the fifth stage the growth of 

 the moth within the larval skin has been steadily advancing. 

 Special nests of epidermic cells, at first quite superficial, form 

 the first rudiments of the future head, legs, wings, and external 

 reproductive organs. These grow dense, take more and more 

 definite shape, and then, finding no room to expand between 



