170 TEXTILE FIBRES. 



The cocoons which have a hard and firm covering are regarded as 

 'the most valuable, as they contain the greatest quantity of silk, while 

 those which are soft and thin are regarded as inferior in quality. 



There are several stages in the life of the silkworm. The first is the 

 egg stage, in which the eggs laid by the female moth are segregated 

 -on the leaf or other material, to which they adhere by an adhesive substance.* 



The eggs are very small and exceedingly light. They have been compared 

 in size and shape to the seeds of the Opium poppy (Papaver somniferum). 



The second or caterpillar stage commences immediately the eggs are 

 hatched. The caterpillars at first are very small, barely more than a 

 quarter of an inch in length. They readily commence feeding on the fleshy 

 parts of the leaves, leaving the veins almost untouched. The body of 

 the caterpillar grows, and the skin covering is renewed several times, to 

 allow for the increase in size, until the larva ceases to eat. 



The third stage is marked by the spinning of the silk fibre from the 

 two opposite glands known as the sericteria. 



The fourth stage is the chrysalis or pupa, which results from a meta- 

 morphosis of the larva in the inside of the cocoon. After a 'period 

 of rest, if undisturbed, it emerges from the cocoon as a fully -developed 

 moth, after having softened a portion of the cocoon. This softening 

 interferes with the commercial qualities of the silk, and to avoid it the 

 cocoons are heated in an oven to about 60 to 70, or immersed in a 

 steam box, which has the effect of killing the pupa or young moth in 

 about ten or twelve minutes. 



The steaming of the cocoons has the effect of softening the silk 

 coating and causing the fibres of the cocoon to adhere together. 



The .cocoon of the female is of an oval shape, and that of the male is 

 more of a dumbbell shape. 



Fig. 110 is a photograph of Bornbyx mori showing the oval cocoon; 

 the eggs laid by the moth in fair quantity, but not adhering together ; 

 also the annulated caterpillar feeding upon the oval leaves of the mul- 

 berry plant. At the bottom of the illustration is the chrysalis or pupa, 

 of an elliptical or oblong shape, conical at one end and rather obtuse at 

 the other, and having a horny and annulated exterior. (This photograph 

 is reduced from a drawing in CasselPs Technical Educator.) 



From the cocoons of Bombyx mori is obtained the ordinary raw silk 

 of France, Italy, China, Japan, and India. The mulberry plant is not 

 much cultivated in England, but grows chiefly in other countries. The 

 Morw alba, or White Mulberry tree, is a native of China. It was intro- 

 duced into England in 1596. At one time a number of plants of the 

 species alba was introduced into Ireland, with a view to the culture of 

 silk in that country. 



