33 [ 175 ] 



inenl. If the cocouu be opened, it is easy to discover the efforts which 

 the insect makes to free itself. When the operation begins, there 

 seems to be a violent agitation in the humors of the little animal; the 

 fluids being driven with rapidity through all the vessels, the limbs 

 and other parts are put in motion, and, by repeated efforts, it breaks 

 through the brittle skin tliat envelopes it. 



Another operation remains to be performed; this is, to penetrate the 

 tough, silky cocoon, with which it is covered. 



It has been a question how the moth escapes from the cocoon. 

 Malphigi* asserts that it first wets the end of the cocoon with a 

 liquid, calculated to dissolve the gum which glues the fibres together, 

 and then employs its head to push them aside, and make an opening. 

 J3ut, as Reaumur has observed, t besides, that so obtuse a part as 

 the head of a moth is but ill suited to act as a wedge, we find the threads 

 not merely pushed to each side, but actually cut asunder. He there- 

 fore infers, that the eyes are the instruments by which the threads 

 are divided — their numerous minute facets serving the purpose of a 

 fine file. The Rev. Mr. Swayne| supports the idea of Malphigi. He 

 informs us that he has unravelled several pierced cocoons, but never 

 found that the thread was discontinued in any one instance. He re- 

 marks, however, that, whenever this is attempted, it must be with the 

 cocoon dry, as the silk will be immediately entangled when put into 

 hot water. Analogy is against the opinion of Reaumur, since other 

 kinds of silkworms make their escape by means of a fluid, as the Jlt- 

 tacus Paphia,oi India, described b}^ Dr. Roxburgh. § Perhaps the 

 two opinions may be reconciled, by supposing that the silkworm first 

 moistens, and then breaks the fibres of the cocoon, by the united aS' 

 sistance of his jaws and head. This is the opinion of Mr. Swayne. 



The time occupied by the silk-caterpillar in going through its dif- 

 ferent forms of existence, varies in different countries; and depends 

 upon climate, the temperature in which they have been kept, food, 

 and the nature of the particular variety of insect. 



These circumstances, which are the true causes, will explain the 

 different statements of various writers on the subject, all of whom pro- 

 fess to speak from actual observation. It will be hereafter seen, too, 

 that the temperature of the room in which the eggs have been kept, 

 fiuring the winter, affects the periods at which they hatch. 



In genera], silk-caterpillars, of four casts, Avhen treated carefully, 

 according to the system laid down by the experienced Dandolo — that 

 is, gradually brought to maturity by a due regulation of the heat of the 

 apartment, experience their first change or moulting on the fourth 

 and fifth days after they have left their eggs: the second commences 

 on the eighth day, and ends on the ninth: the third occupies the thir- 

 teenth and fourteenth days: the fourth, and last, is effected on the 

 twenty-first and twenty-second days. The fifth age lasts ten day?j at 



* De Bombycibus, p. 29. 

 I Reaumur, Hist, des Insects, tome 1, p. 624. 

 % Trans. Soc. Arts, Lond. vol. 7, p. 132. 

 (^ Trans. Linnsan Soc. ^.ond. vol. /, p. 35, 

 5 



