38 THE SILK WORM. 



The Silk Worm undergoes four changes during its 

 brief existence. These are called moultings, and fol- 

 low each other at irregular periods depending on 

 climate, or temperature, and the quality and quantity 

 of the food on which it is fed. The periods of 

 moulting are also hastened or retarded by the high 

 or low temperature in which they have been kept dur- 

 ing the winter. When they have been kept in a reg- 

 ulated degree of temperature, the first moulting takes 

 place on the fourth or fifth day after hatching ; the 

 second on the eighth ; the third on the thirteenth or 

 fourteenth ; and the fourth on the twenty-second or 

 twenty-third. The time intervening between the 

 several moultings is called the several ages of the 

 Worm. The fifth age continues ten days, making 

 thirty two days, at the end of which it ordinarily at- 

 tains its full growth. The time however, has been 

 protracted to sixty days. After it has attained its 

 greatest size, which is about three inches in length, 

 the silk gum is elaborated in the reservoirs, the Worm 

 ceases to eat and soon diminishes in size and weight. 



The vessels in w r hich the silk is elaborated, consist 

 of two parallel tubes of the same size, so very deli- 

 cate, near their termination, as to appear to unite in 

 one ; but by immersing and hardening the insect in 

 spirits of wine, Reaumur found that they continued 

 separate to their ends and that he could take them out 

 entire. By the aid of a microscope he foand that the 

 fibre of silk, minute as it is, has more breadth than 

 thickness, and that in the middle of each fibre there 

 was a kind of furrow, giving it the appearance of two 

 flattened cylinders glued together. 



