Ailanthiculture. 223 
abdominal canal, the “ frass” or excreta becoming moister and paler- 
coloured, longer and conically pointed ; after this a viscid, clearer 
fluid issues from the anus, the last segments of the body being 
porrected for that purpose ; the waxy powder is no longer secreted, 
the caterpillar assumes a yellower tinge, is slightly shrunken, and 
proceeds to find a site for its cocoon. Owing to the large size 
of the full-grown leaflet, one would serve for the purpose of 
several larvz, so that we frequently find two or three cocoons on 
one leaf; generally, however, they choose a medium-sized leaflet, 
and commence their foundation (which subsequently becomes 
what is called the envelope) on the upper surface of the leaflet ; 
frequently, however, they crawl to the end of the leaf, where 
several young and small leaflets are in close proximity, and there, 
commencing on the under surface of these, they connect several 
together. They seem especially partial to the very lowest leaves, 
and many cocoons were there spun, some close to and touching the 
ground. When the ground-work or outer envelope has been 
commenced and coarsely spun along the upper surface of the 
leaflet, the larva traverses the leaf-stalk towards the bough, 
spinning around it a silken tube six inches or more in length. 
Should it arrive thus at the stem of the bough it fastens around it 
the end of the tube and then returns to the ground-work, spinning 
as It goes back; this silken connection between the cocoon and the 
tree on which it hangs is common to many of the Bombycide, and 
is equally spun whether the cocoon is formed on the proper leaf, 
or on a leaf of a weed or Jerusalem artichoke or celery, or is 
formed iu a paper bag, and is evidently spun by design, that when 
the time comes for the leaf-stalk to fall the cocoon may still hang 
secure on the tree, being suspended by the silken thread, and be 
there more safely protected from enemies, especially from mice, 
than if allowed to fall on the ground. Another purpose is gained 
by the insect in suspending its cocoon, viz., the imago is the 
better enabled to expand its wings after its exit from the cocoon, 
which, as I have before observed, is best effected when the moth 
creeps down to the base of the cocoon and there places itself 
with its wings folded downwards over its back, so that their 
own weight helps them to attain their full size.* 
Having first made a ground-work on the upper surface of the 
leaf and completed his silken rope, the larva now returning to 
the envelope strengthens it by stronger threads or shrouds, fixing 
them across the leaf obliquely, so that when the gum dries the thread 
contracts, and the leaf is observed to be curled inwards; the larva 
* Vide supra, p. 202. 
