684 



SILKWORM. 



Covent Garden market at 10s. per ounce ; and care 

 should be taken to obtain them of the proper colour, 

 because those which are of a pale yellow colour are 

 imperfect. The caterpillars are very voracious, as 

 may be observed from the observations of Count 

 Dandolo, given in our article INSECT, vol. ii. p. 837. 

 During this period of its existence it undergoes four 

 moultings, which succeed each other at certain inter- 

 vals, dependent upon the temperature of the weather, 

 or of the places in which the caterpillars are kept, as 

 well as upon the quality and quantity of their food. 

 Thus, if the worms be exposed to a temperature of 

 80 to 100 Fahrenheit, the mpultings will be hasten- 

 ed, and not more than five days required between the 

 third and fourth moultings ; whereas if the tempera- 

 ture be reduced, seven or eight days will be required. 

 The period of the moultings is also regulated by the 

 temperature at which the eggs have been 'kept 

 during the winter. When the heat has been regu- 

 lated, the first moulting takes place on the fourth or 

 fifth day after hatching ; the second in four days 

 more ; the third in five or six days more ; and the 

 last in about eight days. Ten days more are required 

 after this moulting, so that in about thirty-two days 

 after hatching the caterpillar has attained its full size. 

 Rozier, Cours d'Agric. Paris : 1801. Ins. Arch, 

 p. 818. 



When full grown the caterpillar commences the 

 spinning of its cocoon ; and it is this construction 

 which is subsequently employed in the manufacture 

 of silk, as will be more fully shown in the subsequent 

 part of this article. The silk is elaborated in two 

 long slender vessels lying at the sides of the stomach 

 and intestines, and terminating in a single tube, through 

 which the viscid fluid, of which the silken threads is 

 composed, is forced by the peristaltic action of the 

 muscles. This tube terminates in the centre of the 

 lower lip of the caterpillar. Although, however, the 

 two vessels unite into a single tube, it is evident that 

 the silken threads are not united, since we learn from 

 the recent microscopical investigations of Dr. Ure, 

 (Trans. Ent. Soc. vol. i., Journ. of Proceedings, p. 

 50,) that each of the silk threads was found to be 

 composed of two distinct cylinders, which in good 

 silk are found to be perfectly parallel, and quite cylin- 

 drical. The unevenness or the want of parallelism 

 producing inferiority in the raw material. Each of 

 these cylinders varies in diameter from one-two thou- 

 sand two hundredth part of an inch (the measure in 

 silk of the best quality), to one-eighteen hundredth 

 of an inch. When imported, however, several dis- 

 tinct threads are found to be reeled together, which 

 is done by the grower of the silk-worms, the threads 

 being passed through several eyelets, and then wound 

 off. The imported raw silks are of various qualities, 

 depending upon .the mode and time of feeding, as 

 well as upon the food of the silk-worms. These com- 

 pound threads are one-five hundredth part of an inch 

 in diameter, each being divisible into eight threads ; 

 that is, into four pairs of cylinders in the best silk. 

 The specific gravity of silk is, according to this au- 

 thor, greater than had been generally considered, be- 

 ing 1256 to 1000, and consequently greater than the 

 strongest muriatic acid or water. 



The cocoon consists of three distinct layers of 

 silk ; the first is loose and flossy, and is unserviceable 

 for the silk manufacture ; the second is closer, the 

 silk crossing from side to side ; and the third is still 

 finer, and is glued strongly together, so as to form a 



compact inner coating ; of course the more silk which 

 is employed in the construction of the outer floss 

 covering, the inner coatings are diminished in thick- 

 ness ; and, acting on this principle, M. Hoffmann, of 

 Munich, has informed the writer hereof that he has 

 succeeded in obtaining considerably more than the 

 ordinary supply of the middle layer, by placing the . 

 worms, when full grown, in very confined situations, 

 their instinct informing them that, in such case, there 

 is no necessity for a floss coating of the ordinary 

 thickness. When this cocoon is completed, the in- 

 closed caterpillar again casts its skin, with the head 

 and jaws attached to it, when it appears under the 

 form of a conical chrysalis of the ordinary shape. At 

 first the chrysalis, when opened, appears to consist 

 only of a yellowish mucus, but by degrees the vari- 

 ous parts of the future moth acquire their proper con- 

 sistence ; and in about a fortnight or three weeks a 

 slight swelling of the chrysalis indicates the approach 

 of another change ; a rupture down the back succeeds, 

 and, by degrees, the moth bursts through its horny 

 coating into the hollow chamber of the cocoon. 

 The moth subsequently emits a fluid, which has the 

 effect either of dissolving the gum or the threads at 

 one end of the cocoon, and soiling that part where 

 the moth makes its escape. This of course is a 

 circumstance which would be injurious to the interest 

 of the silk grower, and is remedied in the manner 

 subsequently described. Previous to the egress of 

 the perfect insect, the cocoon may be wound off 

 without any interruption of the thread, so that it is 

 evident that the whole is spun continuously by the 

 caterpillar ; the length of the thread in a cocoon 

 varies from six hundred to a thousand feet, and the 

 whole does not weigh more than three grains and a 

 half ten thousand cocoons scarcely averaging so 

 much as five pounds in weight. An ounce of eggs 

 will produce about 40,000 caterpillars, which will 

 consume 1073 Ib. of leaves, and produce from 80 to 

 100 Ib. of cocoons, or about 8 Ib. of raw silk. 



The perfect insect is remarkable for its dull and 

 stationary habits ; indeed, it can scarcely be said to 

 possess the powers of flight. In this respect a simi- 

 larity of manners exists also in the caterpillar, which 

 does not wander away from its food, although uncon- 

 fined ; and it has been well remarked by Mr. Sells, 

 that these interesting peculiarities materially favour 

 the easy management of the insect, and beautifully 

 harmonise with the consideration of its vast import- 

 ance to mankind. 



The history of the silk manufacture, and its intro- 

 duction into this country, require some notice in a 

 work like the present. The insect is an inhabitant 

 of China, although now perfectly naturalised in other 

 countries ; and the Chinese are supposed to have 

 discovered the art of making silk 2700 years B.C., 

 when the Empress Si-ling-chi is said to have first 

 observed the labours of the silk-worms on wild mul- 

 berry-trees, and applied their silk to use. From 

 China the art passed to Persia, India, Arabia, arid 

 the whole of Asia. According to Latreille, the city 

 of Turfan, in Lesser Bucharia, was for a long period 

 the rendezvous of the caravans coining from the East, 

 and was the chief depot of the silk-trade of China. 

 It was the metropolis of Seres, in Upper Asia, or of 

 Serica of Ptolemy. The expedition of Alexander 

 into Persia and India first introduced the knowledge 

 of silk to the Grecians, 350 years B.C., and. with the 

 increase of wealth and luxury in the Grecian court, 



