closely grouped in pairs, readily distinguished from each other by their relative positions.
The pair situated nearest to the. anus may be denominated the superior spinners; that furthest
removed from the anus, the inferior spinners; and the mammulae placed between these
extremes, the intermediate spinners; distinguishing them, when there are two pairs, by
prefixing the terms superior and inferior. Fine, moveable papillae, differing in size in the same
individuals, are situated at the extremity, or distributed along the inferior surface of their
terminal joint, whence issues the viscous secretion of which the silken lines produced by
spiders are formed.1
The superior pair of spinners, when triarticulate and considerably elongated, has been
mistaken by Treviranus and other skilful zootomists for anal palpi. This singular error may
be attributed to the peculiar disposition which the papillae, or spinning-tubes, connected with
the superior mammulae, when thus modified, commonly exhibit. Arranged along the under
side of the terminal joint, they present the appearance of slender hairs dilated at the base;
but if the spinners, when they are in operation, be carefully examined with a powerful
magnifier, the function of the hair-like tubes may be ascertained without difficulty, as the fine
lines of silk proceeding from them will be distinctly perceived. The purpose subserved by
the superior mammulae, when very prominent and composed of several joints, is the binding
down with transverse lines, distributed by means of an extensive lateral motion, the threads
emitted from the inferior mammulae; by which process a compact tissue is speedily
fabricated.8
On the under part of the abdomen, near its anterior extremity, there are two or four
either slightly pubescent or naked plates of a whitish, yellowish, or brownish hue, having at
their posterior margin a narrow, transverse orifice or stigma, communicating with the organs of
respiration.. In the space intermediate between these plates the external aperture of the sexual
organs is situated in female spiders. It is fully developed in the adult state only.
The internal organs of respiration in connexion with the anterior pair of stigmata present
the appearance of membraneous sacs formed by lamellae applied to one another like the leaves
of a book; each of these little receptacles opens into a common cavity, the membraneous
margins of which adhere to a cartilaginous arc connected with the branchial operculum.
These organs are common to all spiders, and, from the important function they perform, may
be termed pulmonary branchiae. The posterior pair of stigmata occur much less frequently,
and in communication with them there are numerous tracheae which radiate to the surrounding
parts.A
n elongated, fusiform vessel, whose office is analogous to that of the heart in animals
of a higher order, extends along the middle of the superior region of the abdomen, immediately
beneath the integument, on which account it has been named the dorsal vessel. An artery
is continued from both its extremities, and the colourless blood, which is returned to it by
several veins on each side, is propelled forwards by the contraction of its muscular walls.
The alimentary canal communicates with the mouth, between the maxillae, by a short,
slender oesophagus of a delicate texture, terminating in the stomach, which is placed in the
posterior part of the cephalo-thorax. The digestive tube then continues as a straight narrow
, 1 * Transactions of the Linnean Society,’ vol. xviii, pp. 219-224.
8 * Researches in Zoology,’ p. 298, et seq.
canal, of moderate length, which dilates and adheres by its parietes to a kind of epiploon,
filled with adipose granules, situated in the abdomen. Posteriorly the dilated part becomes
stronger in texture, insensibly contracts, and then undergoes a second dilatation before it
opens into the rectum.
Spiders employ their falces to seize, kill, and retain the insects that they prey upon, and
their maxillae to masticate them and to express their fluids, which, when mingled with the
liquid contents of the stomach, previously propelled into the mouth through the minute
pharyngeal aperture, they swallow. Though extremely voracious, they are capable of enduring
long abstinence from food, a female Tkeridion quadripunctatum having been known to exist for
eighteen months without nutriment in a phial closely corked.1 When affected by thirst they
will drink water freely. Their faeces consist of a white liquid containing oval, black particles
of a greater degree of consistency.
It has been already remarked that the aperture of the generative organs is situated
between the branchial opercula in female spiders. At this part, which is often provided with
opercular pieces of a more or less solid texture, the oviducts terminate. In the house spider,
Tegenaria domestica, these oviducts are continued internally in an insensible manner with the
ovaries, which form on each side of the intestinal canal a kind of sac, to whose parietes the
ova are attached in a racemose manner. In the diadem spider, JEpeira diadema, each ovary
is divided by a transverse septum, and the eggs are laid at distinct periods.
With regard to the function exercised by the remarkable organs connected with the
digital joint of the palpi of male spiders there exists some difference of opinion. Taking
anatomy as his guide, Treviranus arrived at the conclusion that the parts in question are used
for the purpose of excitation merely, preparatory to the actual union of the sexes by means of
appropriate organs situated near the anterior part of the inferior region of the abdomen.
This view of the subject, which is very generally adopted, is opposed to that derived from
physiological facts by Dr. Lister and the earlier systematic writers on arachnology, who
regarded the palpal organs as strictly sexual, and recent researches, conducted with the
utmost caution, have clearly established the accuracy of the opinion advanced by our
distinguished countryman.8
There are in the posterior part of the abdomen of spiders special organs for the secretion
of the viscous matter of which their silken lines are formed. These consist of intestimform
vessels, varying in number and extent in different species, and having near their base, not far
from the point where they1 open, into the spinningtmammulas, some small, supplementary
canals'. When issuing, from the minute papillae connected with the mammulae, the viscous fluid
hardens immediately on exposure to th e action of the air, forming delicate filaments, which
vary greatly in number in different species, Those of each mammula unite in the first
instance, and then the whole combine to form a common thread; so that the lines which
serve such important purposes in the economy of spiders are composed of numerous filaments
of extreme tenuity.
The nervous system in spiders is ganglionic. A bilobed ganglion, situated in the anterior
.. ;:1 ‘ Researches in Zoology,’ pp. 302, 303.
8 ‘ Report of the Fourteenth Meeting of the British Association for the Advancement of Science,’
pp. 67-69.