SILK-WORMS. 241 
course requiring care and attention, without which 
no species will thrive. 
As 600 cocoons of this species weigh a j>ound 
and a half, and that 360 of the common cocoon 
make the same weight, it is thought that the 
worms that produce the 600 cocoons eat more 
than the common species ; but my experiments 
shew this to be erroneous. 
2. Of the large Silk-worm of Four Casts. 
I reared many of these silk-worms of a very 
large quality also separately. The eggs came 
from Frioul: although these eggs produce larger 
worms and larger cocoons than the common spe- 
cies, yet are they not either much larger or much 
heavier ; they are only one-fiftieth more in 
-weight ; 37,440 eggs of Frioul weigh an ounce, 
whilst 39,168 eggs of the common sort make an 
ounce. 
The worms proceeding from the Frioul eggs, 
weigh, when at their utmost size, nearly twice 
and a half as much as the common worm. The 
cocoons are in the same proportion ; 150 of the 
large sort weigh a pound and a half, while it re- 
quires 360 of the common cocoon to weigh as much. 
The only advantage they may offer, is that 
I 84 lbs. of leaves will produce 1 ^ lb. of cocoons, 
whilst 20 4 lbs. of leaves are required, to produce 
M 
