Silkworm from Japan. 417 
destroy all chance of a future brood. But since under the care 
of man these results are mostly prevented, it becomes our aim to 
economise trouble, by hatching out nearly at one time all the 
brood. Hence Mons. Chavannes recommends to separate the 
male and female cocoons, to retard the former and hasten the 
latter. The following is his method for determining the sexes of 
the cocoons: since the females which carry eggs are the largest 
and heaviest, he advises to weigh, say 100 cocoons, then divid- 
ing the whole by 100 he obtains the mean weight of a single 
cocoon; the female cocoons will then weigh a little heavier, and 
the male cocoons lighter than this. Many of the machines for 
weighing letters will easily perform this office, if suitably 
weighted. 
About forty days from the commencement of the cocoon the 
moth emerges. Mons. Personnat recommends a_ peculiarly 
formed cage (la cage oblongue) for the purpose of fecundation and 
deposition of eggs, and he advises to suspend the cocoons in this 
cage on the thirtieth day. The cage is a frame of wood 
covered with canvass or coarse muslin, old and rubbed lest the 
fine threads should annoy the moths; the muslin is dipped in a de- 
coction of tan, which colour is believed to be agreeable to the 
moths; the wood is also dyed; tan is employed to keep off by its 
smell noxious insects. The cage is straight and of any convenient 
length, the bottom is 12 inches wide, the sides 20 inches high, and 
the top 22 to 26 inches wide; hence it follows that the sides 
slope outwards from the bottom to the top, and this slope favours 
the moths at rest, either when just emerged or during coition, or 
when depositing their eggs ; the ends of the cage are sloped in like 
manner. He has observed that if not sloped the moths, after passing 
a night within and flying about in pursuit of one another, have lost 
the hooks from off their feet, especially the females; these lie 
exhausted at the bottom of the cage and die before they can lay 
their eggs; whereas if the sides are sloped, the body of the female 
being supported, they retain their strength much longer. On the 
top he arranges a little opening, closed by a canvass door, situate 
every forty inches, in order to obtain access to the interior to 
remove empty cocoons and dead moths. It is found to be con- 
venient to suspend in the interior in two rows at an equal distance 
from each other and from the sides, every 10 inches apart, a loop 
of grey string, strong enough to allow of the moths clinging to it. 
On these he has often witnessed coition taking place, and eggs 
are often deposited thereon. Lastly, in a corner a sponge full of 
