STATES OF INSECTS. 217 



wound off, and is known in commerce by the name ofjloss 

 silk. 



Manoeuvres in their general principle similar to those 

 of the silk-worm are followed by most of those larvae 

 which inclose, themselves in silken cocoons. Many spe- 

 cies, however, adopt variations in the mode of procedure 

 all of which it would be tedious to particularize, but some 

 of them are worth mentioning. The larvae of Tortrix 

 prasinana, and other species of moths which form co- 

 coons resembling a reversed boat, arrange their threads 

 in layers, so as to construct two parallel walls gradually 

 inclining towards the top and ends, where they finally 

 force them to approach each other by means of an appa- 

 ratus of silken cables a . And the larva of Saturnia Pavo- 

 nia, though it forms the base of its flask-shaped cocoon by 

 spinning like the silk-worm a number of interwoven zig- 

 zags, places the threads which compose the interior fun- 

 nel-like opening of the apex nearly straight, parallel to 

 each other, and converging towards the same point in 

 the centre b . 



These last, as well as almost all larvae, constantly re- 

 main in the inside of the cocoon during its construction. 

 But De Geer has given us the history of a minute cater- 

 pillar of a species of moth [Tinea L.) which feeds on the 

 under side of the leaves of the Rhamnus Frangula, or 

 Black Alder, that actually weaves half of its cocoon on the 

 outside. This cocoon, which is very small, is beautifully 

 fluted, consisting of several longitudinal cords, with the 

 intervals filled by fine net-work, and shaped like a re- 

 versed boat c . The animal begins by laying the founda- 



a Reaum. i. 555—. h Plate XVIJ. Fig. 5. b. 



c De Geer i. t. xxxii./. 3—6. 



