234 



THE INSECT WORLD. 



becomes smaller and smaller. We are still in a state of utter igno- 

 rance as to the cause of this last affection, which has occasioned, for 

 ihe last ten years, incalculable losses in the rearing houses, which 

 threatens the silkworm with complete destruction, and which in the 

 meanwhile has ruined the unfortunate countries of the Cevennes, the 

 principal seat of sericulture in France. 



During the fifth age, the worms become large so quickly that on 

 die fifth or sixth day they are obliged to be moved away from each 

 •other on the litter. The dillteniciit must be made every two days, or 

 indeed, every day now, on account of the enormous amount of the 

 excrement; and, at the same time, a good ventilation must be con- 

 stantly maintained. The temperature of the room should now be 

 kept to 24°, without ever exceeding this degree of heat. When it is 



Fi-. 



.— Sprigs of heather arranged so that Silkworms may mount hito them. 



perceived that the worms wish to ascend, or luoinit, there are placed 

 •on the tables, at certain distances from eacli other, little sprigs of 

 heather or very dry branches of light wood. 



When the worms begin to mount into the heather, one must 

 ■ cncabaner — that is to say, form with these branches little hedges, 

 curved back like a hut or cradle, the openings of which are, on an 

 average, seventeen inches or so (Fig. 213). At the expiration of ij 

 twenty-four hours all the good worms have mounted. The laggards 

 who remain under the cabanes are taken off by hand, and placed on a 

 table, which is immediately encabanea. 



The cocoons spun on these branches of heather ought to be 

 large, heavy, and well-shaped. The good cocoons are regular ; their 

 ends are rounded and not pierced ; and they are hard, especially at l| 

 their extremities, and have a fine grain. They are cylindrical. The 

 best are drawn in towards the middle, or have a concavity on either 

 side of it (Fig. 215). P:very one knows that there are white and 

 yellow cocoons. They are the produce of different races of worms. 



