46 AMERICAN SPIDERS AND THEIR SPINNINGWORK. 
which the spider’s spinningwork is composed. The ordinary spinning 
spool is a hollow, cylindrical, chitinous formation, and consists of two 
joints: first, a shorter or longer basal cylinder, bj, whose walls are strongly 
brown colored; and second, a much smaller and transparent ter- 
minal joint, tj, which terminates in a very fine point, provided 
with a minute opening. The spools in which the pyriform 
glands terminate, s.ss and ls, Fig. 24, stand in large number on all the 
spinning fields. They are not alike in form of the several spinnerets, 
and those of the anterior spinneret especially, are quite differently con- 
structed from those of the posterior pairs. 
On those spools of the posterior spinnerets 
which receive pyriform glands, the basal 
joint (Fig. 39, bj) forms everywhere a reg- 
ular cylindrical tube of even 
thickness, which seems to be 
obliquely cut at the exterior end 
where the terminal joint is united to it. 
This interrupted space is, as Fig. 39 (i.s) 
shows, a very little flat in the middle, and 
towards the edge slightly curved. The base 
of the tube is joined to the surface of the 
spinneret by a ring formed enlargement, 
and, as elsewhere, bristles and hairs with 
chitinous rings are seated upon the skin. 
Into the base of each spool enters a 
Spinning 
Spools. 
Pyriform 
Spools. 
Fic. 39. Fia. 41. Fie, 40. 
Fic. 89. Spinning spool of the usual form 
from the posterior spinneret, and connected 
with pyriform glands. Multiplied greatly, 
2000 times. Fic. 40. Spinning spool from 
the anterior spinneret. 2000. Fig. 41. 
Spinning cone or spigot into which a cylin- 
drical gland empties. The whole taken 
from the apex of the middle spinneret. 
> 2000 times. bj, basal piece; c, circumfer- 
ence or ring of the chitinous wall of the 
basal piece, constituting a ring formed 
chitinous thickening on its apex; em, the 
exterior membrane of the chitinous wall 
of the duct, du, with vertical striation; im, 
inner membrane of the duct passing into 
the canal of the basal piece. 
single duct of a pyriform gland, and this 
duct can be followed as a straight tube 
to the end space of the base of the spool, 
where it ceases to exist as a canal, and is 
merged into the cavity of the terminal 
joint. 
The terminal joint (tj) is in the larger 
tubes, about half the length of the basal 
joint, bj, and sits precisely in the centre 
of the summit of the basal joint. The 
terminal joint is hollow, gradually diminishes, and terminates in a very 
fine, round opening at the tip. The thickness of a single thread, coming 
from this spinning spool, would be about 0.001 mm., or one twenty-five- 
thousandth part of an inch. This form of spinning spool undergves 
changes at different places of the spinning field, caused by the basal cylin- 
der varying in length. The central parts of the spinning field especially 
are covered with very short spools. The terminal joint, however, remains 
unchanged in length, notwithstanding the varying lengths of the basal 
joint. (Fig. 39.) 
se 
