XIV ORB-WEBS 349 
venomous jaws of its captor. Sometimes the insect is so power- 
ful, or the spider so sated with food, that the latter hastens to 
set free the intruder by biting away the threads which entangle 
it before much havoc has been wrought with the net. 
The viscid matter on the spiral line dries up after some 
hours, so that, even if the web has not been destroyed by insects 
and stress of weather, this portion of it must be frequently 
renewed. Commencing a new web is, as has been seen, a 
troublesome matter, and it will readily be understood that the 
spider prefers, where practicable, to patch up the old one. This 
is done by biting away torn and ragged portions and inserting 
new lines in their place. 
The part played by the various spinning glands in the con- 
struction of the orb-web may be briefly stated.’ The ampullaceal 
glands furnish the silk for the foundation lines and radu. The 
spiral has a double ground-line proceeding from the middle 
spinnerets, but it is not quite certain whether it proceeds from 
the ampullaceal or the tubuliform glands. The chief function of 
the latter, in the female, is to furnish silk for the egg-cocoon. 
The viscid globules are the products of the aggregate glands. 
The aciniform and piriform glands provide the multitudinous 
threads by which the spider anchors its various lines and enwraps 
its prey. 
Some Orb-weavers always decorate their snares with patches 
or tufts of flossy silk. In the snare of the North American 
Argiope cophinaria the hub is sheeted, and from it extends down- 
wards a zigzag ribbon of silk stretched between two consecutive 
radii. Vinson” discovered a remarkable use for similar zigzag 
bands in the web of the Mauritian spider, Lpeira mauritia. It 
furnished a reserve supply of silk for enveloping partly entangled 
insects whose struggles were too vigorous to succumb to the 
rather feeble threads which the spider was able to emit at the 
moment of capture. The spider was able to overcome a grass- 
hopper much more powerful than itself by dexterously throwing 
over it with one of its hind legs a portion of the ribbon of silk 
which it had thus stored up for emergencies. 
Many orb-webs are defective, a sector of the circle being 
uniformly omitted in the structure. The genus Hyptiotes does 
1 See Warburton, Quart. J. Mier. Sci. xxi., 1890, p. 29. 
” Aranéides de la Réunion, Maurice et Madagascar, Paris, 1863, p. 238. 
