[Illustration: Fig. 213.--Sprigs of heather arranged so that Silkworms may mount into them.]
When the worms begin to mount into the heather, one must _encabaner_--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 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 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). Every one knows that there are white and yellow cocoons. They are the produce of different races of worms.
Commerce recognises two kinds of white silk: the _first white_ and the _second white_. The silk of the _first white_ is produced by the race _Sina_, the cocoons of which are of a perfect and azured white. They produce the most beautiful and most precious silk, and serve for the fabrication of light and delicate coloured tissues. The silk of the _second white_ is furnished by two races: the _Espagnolet_ and the _Roquemaure_.
[Illustration: Fig. 214.--Spherical cocoon of the Bombyx mori.]
[Illustration: Fig. 215.--Cocoon of Bombyx mori, drawn in towards the middle.]
The races that produce yellow cocoons are more numerous than the white ones. The yellow races are divided into three groups: those that have small, middle-sized, or large cocoons. The first and second are stronger, and more esteemed than the last.
The greater number of the races of silkworms have, let us here mention, white and yellow cocoons; there are some, however, whose cocoons are of a greenish white, or even quite green, or of a reddish green. One race, raised in Tuscany, near Pistoia, has cocoons of a pale rose colour; and, lastly, mention has been made of cocoons of a purple colour.
When the cocoons are completed, the people in charge of the rearing establishments separate them from the heather and sell them to the silk-spinners. But they must manage to get these cocoons into a state in which they will remain entire during a long time. They must, in other words, kill the chrysalis, to prevent the cocoons being pierced by the moth. To kill the chrysalis so as to prevent the development of the imago is an operation which is called the _étouffage_, or stifling.