222 STATES OF INSECTS. 



besides these more general colours, some cocoons are 

 black a , some few blue or green, and others red b . Some- 

 times the same cocoon is of two different colours. Those 

 of certain parasites of the tribe of Ichnenmones minuti L. 

 the motions of one of which I noticed on a former occa- 

 sion c , are alternately banded with black or brown and 

 white, or have only a pale or white belt in the middle, 

 which gives them a singular appearance. In both cases 

 the difference in colour depends upon the different tints 

 with which the silky gum is imbued in the reservoirs : 

 the first portion of it is white, and with this the larva 

 first sketches the outline of its cocoon, and then thickens 

 the layers of silk considerably in those parts where the 

 white bands appear : when these are finished, its stock 

 of white silk is exhausted, and the remainder of the inte- 

 rior of the cocoon is composed of brown silk d . The cir- 

 cular operculum above mentioned as covering an acorn- 

 shaped cocoon, is paler than the latter, and also orna- 

 mented by a zone within the margin of deep brown. 

 The pale cocoon also of Attacus Paphia is veined with 

 silk of a deep red. 



I have very little to say on the substance of the silk of 

 cocoons. Though that of the silk- worm is composed of 

 such a slender thread, that of many others is still finer, 

 scarcely yielding in tenuity to the spider's web. On the 

 other hand, the silk of the cocoons of Saturnia Pavonia 

 and of several foreign species is as thick as a hair. 



With regard to the texture of their cocoons— in some, 

 as in that of the silk-worm, the threads are so slightly 



3 I have a black one from Mr. Francillon's cabinet. 



b W. Diet. d'Hist. Nat. vi. 294. 



See above, Vol.. II. p. 298—. d Reaum. ii, 436. 



