Thread nets, which were of great use, have been supplanted lately, with great advantage, by paper ones, which were invented by M. Eugène Robert. These are leaves of paper, of a peculiar manufacture, pierced with holes proportioned to the size of the worms which are to pass through them. The paper net can be used advantageously also for separating the worms that are too near together, or, as they say, for the _dédoublement_. Formerly, the _délitement_ and the _dédoublement_ were done by hand--a tedious work, and one that presented serious disadvantages. Now-a-days, as we have seen, the worms themselves perform these two perilous operations. At the second age they still cut the leaves for the worms, but into larger pieces, and proportioned to their size. During the day the temperature of the room ought to be kept to 21° Centigrade, but it may be lowered by 1° or 2° during the night. Towards the end of this age they have only four meals. When the worms are on the point of going to sleep, their meals are decreased. [Illustration: Fig. 211.--Lozenge-shaped net.] [Illustration: Fig. 212.--Square net.] During the third age the number of the meals is kept to four, the first being given towards five o'clock in the morning, and the last between ten and eleven o'clock at night. The leaf is cut into much larger pieces, and distributed as equally as possible. The _délitement_ and the _dédoublement_ are proceeded with as in the preceding age. One begins to find pretty often during this period of the life of worms, some _luisettes_--that is to say, worms which have not strength enough to moult. They are larger than those just woke up, and that have not as yet eaten, and are shiny. They must be carefully removed, for they will not be long before they die, and infect the air of the room. During the fourth age they no longer cut the leaves, but give them a great deal more at once. The result is that the litters increase in thickness, and that the _délitement_ must be performed oftener; for the rest, four meals are always necessary. Many _luisettes_ may be seen during the fourth age. The moult which follows the fourth age is the most critical phase in the life of the silkworm. During their sleep they are a prey to acute suffering, and are plunged into a state of lethargy which resembles death. The dryest and cleanest litters diffuse very soon a sickly smell. This moult lasts from thirty-six to forty-eight hours. During this time the room should be kept to at least 22° Centigrade.