PEOCEEDINGS OF SOCIETIES.
129
deposition of moisture does, however, frequently occur upon
their surfaces whilst shells are undergoing examination, in
which case it would be a safe precaution to allow them for
awhile to remain exposed to the air before returning the
drawer to the cabinet."
September 25th, 1858.
On the Anatomy of the Spinning Organs of the Araneidm.
By Mr. R. H. MEADE:
THE tegumentary covering of the abdomen in true spiders
consists of three layers, viz.: 1st, an external, horny, transparent membrane, more or less densely clothed with hairs;
2d, an intermediate soft stratum of pigmentary matter; and
3d, an expanded network of muscular fibres, which will
enable the spider to compress the contents of the cavity.
The spinnarets, seated near the apex of the abdomen, at the
under side, are mostly six in number, placed in three pairs—
an anterior, a posterior, and an intermediate pair. The posterior pair is often prolonged and tri-articulate, when the
spinners composing it have been called anal palpi. There is
a fourth pair of spinnarets in Mr. Blackwall's family of the
" Cinifloridse," situate in front of the ordinary anterior pair.
They are short, compressed, and inarticulate. The spinnarets are connected with the surrounding integument by
means of diverging bands of muscular fibres, which enable
them to move in various directions. In the interior of the
abdomen, nearer the base than the apex, there is a point
(opposite the orifice of the oviduct in the female), from
which several muscular bands radiate in various directions, keeping the different abdominal organs in their
places. Some are inserted into the integument on both the
dorsal and ventral surfaces of the abdomen; others run
backwards in straight parallel bundles, and pass into the interior of the spinnarets. These last bundles have their fibres
strongly striated, like the strong muscles connecting the legs
with the cephalo-thorax. The other muscles mentioned are
only faintly marked. The interstices between the organs
in the abdomen are filled with adipose matter, connected
into lobules by fine cellular tissue. This serves as a reservoir
of nutriment, and enables spiders to bear very long abstinence. The glandular organs, which secrete the silk, consist of a number of sacs or bags and convoluted or branched
tubes, of various sizes and shapes—each furnished with a distinct excretory duct, which terminates separately on the sur-
180
PROCEEDINGS OF SOCIETIES.
face of the spinnaret, so that there is no communication
between one and another. The spinning glands may be divided into four varieties. The first consists of a large
number of exceedingly minute cells, each containing a kind
of nucleus, and furnished with a very fine duct. These are
only found in the family of the Cinifloridse, and are placed
immediately beneath the integument, near the supplementary spinnarets, with which they are connected. These
glands evidently secrete the fine silk, which forms the flocculus in the web of Cinifto (Clubiona) atrox and feroar. The
next group of spinning glands is the most numerous and
most constant of all the varieties. It consists of an immense
collection of small oval, or fusiform,, cells, with fine elastic
ducts, which terminate principally in the anterior and posterior pairs of spinners. These probably secrete the fine
threads, which weave the more delicate parts of the webs,
and construct the cocoons in which the eggs are deposited.
The third variety of silk glands contains several cartilaginous
sacs, or convoluted tubes, of a firm or even hai'd consistence,
but brittle and transparent. These are often of a large size,
especially in the different species of Epeira. They have fine
inelastic ducts. Perhaps these secrete the adhesive lines
Avhich are placed on the geometric webs of spiders. The last
and most interesting kind of glands are membranous sacs
and tubes, some vermiform, others clavate, others furnished
with branched caeca. They vary in size, some being very
large. All have thickened and apparently fibrous walls, and
they are all furnished with elastic ducts, having a fibrous external coat, composed of distinct rings, which break up into
separate pieces when the duct is stretched. From their construction, these sacs and ducts must possess a strong contractile and expulsive power. They probably secrete the stronger
threads, which are stretched between distant points, and
form the framework of the webs; and they must also produce the gossamer of the aeronautic spiders, for they are
exceedingly large and numerous in hycosa saccata and
Thomisus cristatus—common aerial species—which require
them for no other purpose, as they do not spin ordinary
webs, being erratic in their habits. In most other species of
Lycosa, also, the spinning organs are very slightly developed.
The ducts from both the cartilaginous and membranous
glands terminate in all the three ordinary pairs of spinnarets ;
several from the latter may be traced into the long triarticulate spinnarets of Agelena labyrinthica.