STRUCTURE AND ECONOMY OF SPIDERS, 307 
of the limbs, the spider is ultimately enabled to 
accomplish its purpose. The spines with which the 
legs are provided no doubt contribute greatly to 
facilitate the operation; for, as they are directed 
down the limbs, and are movable at the will of the 
animal, when it has partially withdrawn the legs from 
their sheaths by contracting them, it can prevent 
them from reentering by slightly erecting the spines, 
and thus bringing their extremities in contact with 
the inner surface of the integument. When the 
spider has completely disengaged itself from the 
slough, it remains, for a short period, in a state of 
great exhaustion, suspended solely by a thread from 
the spinners connected with the interior of the 
abdominal portion of the cast skin, which is much 
corrugated and drawn together. The entire pro- 
cess, as above described, occupies the space of about 
twenty minutes. After reposing a little, the spider 
further attaches itself to the suspensory lines by the 
claws of the feet; and when its strength is suffi- 
ciently restored, and its limbs have acquired the 
requisite degree of firmness, it ascends its filaments 
and seeks its retreat. 
Having frequently witnessed the moulting of 
spiders in their natural haunts, and also in a state 
of captivity, and having carefully examined the cast 
skins of numerous species belonging to the genera 
Dysdera, Segestria, Clubiona, Drassus, Tegenaria, 
Textrix, Theridion, Neriene, Pachygnatha, Linyphia, 
x 2 
