106 NATURAL HISTORY. [cH. V. 



of the cultivation of this large species are manifest ; 

 the silk is coarser; their life being four or five days 

 longer, the labourers must be kept longer ; the ex- 

 pense and the risks are therefore greater ; and the 

 accidents attending the mulberry-tree will also be 

 thereby multiplied. 



It has been stated, that 39,168 eggs of the com- 

 mon silkworm weigh an ounce. If each egg pro- 

 duced a worm, and each worm came to maturity, 

 an ounce of eggs should yield 1G2 lbs. of cocoon. 

 This is in conformity with Count Dandolo's .expe- 

 rience, under his improved mode of rearing the silk- 

 worm. Latreille, however, gives a very different 

 result, "Formerly, he says, an ounce of eggs pro- 

 duced 80 or 100 lbs. of cocoon, ten or at most twelve 

 pounds of cocoon yielding a pound of silk. But for 

 some time the ounce of eggs has scarcely yielded 

 thirty or forty pounds of cocoon, and fifteen or six- 

 teen pounds of cocoon yields but a pound of silk. 

 This difference he attributes to the injudicious 

 selection of eggs. 



A perfect egg or grain, as it is termed, should be 

 of a dark slate-colour. There are different modes 

 adopted to hatch them. In the south of France 

 they are enclosed in cotton, and carried by the wo- 

 men between their petticoat and chemise during the 

 day, and at night placed in the same bed with them. 



The spontaneous hatching of eggs by means of 

 the natural heat of the atmosphere, is of course out 

 of the question in climates as variable as those of 

 Europe. During the hatching of the eggs, the tem- 

 perature of the stove-room in which the worms are 

 to be developed should be at least 61'^, andjhis 

 should be gradually increased up to 75^, in which 

 degree of warmth the young worm is to be kept 

 until the first cast or moultmg. The heat during 

 the second cast should be between 73° and 75°, be- 

 tween 71° and 73° till the third, and lastly, betweci/ 

 68° and 71° till the fourth. 



