Page:Encyclopædia Britannica, Ninth Edition, v. 2.djvu/315

SPIDERS.] ARACHNIDA 295 Jlenge s and Ausserer s statement : "A male Agelena labyrinthica confined in a phial, spun a small web, and among the lines of which it was composed I perceived that a drop of white milk-like fluid was suspended ; how it had been deposited there I cannot explain, but I observed that the spider, by the alternate application of its palpal organs, speedily imbibed the whole of it." That the spermatic fluid is conveyed to the female parts of genera tion by the male palpi is thus pretty certain ; and it seems not improbable that there are more modes than one by which the palpi are supplied with the fluid. See also critical observations on this subject by Dr. T. Thorell, 1873, Synonyms of Eur op. Spid. pp. 591- 595. Before concluding our remarks on the internal structure of the Araneidea, two of their special properties must be shortly noticed the secretion of the poison injected into the wounds made by the fangs of the falces, and the secretion of the matter emitted as silken threads through the spinning organs. The poison is secreted in two small elongated sacs (one for each of the falces), situated within the cephalo- thorax on either side of the alimentary canal; the sacs are connected with a membranous channel in each of the falces, the channel running completely through the fang, from an orifice near the end of which the poison is pressed out by the spider in the act of wounding its prey. On the venomous nature of the poison some remarks have already been made. As to its venom in British spiders, see " BlackwalPs Experiments," Trans. Linn. Soc., xxi. pp. 31-37. The result of these interesting experiments is contrary to the generally received idea as to the great virulence of spider poison. The external spinning organs have been mentioned above; they are usually called spinners, and are various in size, both actual and relative, in form and in structure, as well as in number. From the extremity of each of these organs the silk matter issues through numerous movable papilla, or spinnerets, which are similar to hollow bristles with enlarged bases ; the papillae vary both in form and number in dif ferent species, and from each spinneret or papilla issues an exceedingly fine thread ; this, uniting with threads from all the other papillae, forms the ordinary silk line, which though to ordinary observation simple, is composed of num berless threads from some one, or all, of the spinners. The matter from which the silk is formed is secreted in organs (silk-glands) situated within the ventral surface of the hinder part of the abdomen. These glands vary in number, size, and form in different species ; they differ also in size and shape in the same species, for the secretion of different qualities of silk-matter ; and each gland has a distinct duct terminating at the extremity of the spinners. The emission of silk matter appears certainly to be a voluntary act on the part of the spider ; but it is a disputed question among arachnologists, whether spiders have the power forcibly to expel it, or whether it is merely drawn from the spinnerets by some external force or other. Mr Blackwall (Trans. Linn. Soc., xv. p. 455 ; Researches in Zoology , pp. 242-248, and History of Spiders of Great Britain and Ireland, p. 12) is of the latter opinion ; while Mr R. H. Meade (of Bradford, Yorkshire), in Report of British Assoc., 1858, pp. 157-164, pi. 16, thinks that (from microscopic anatomical investigations which he has himself made) there is good evidence of spiders having the power to expel it, for he finds a certain muscular arrangement which would apparently suffice to give this power, and observers have actually seen the lines propelled. Mr Meade, however, need not be assumed to assert an indefinite power to expel threads of silk to any indefinite distance. The truth probably is, that spiders have, and do exercise, a general power not only of emitting silk matter from the secreting glands merely to and from the external orifices of the silk- tubes, but also of propelling it when necessary to some short distances; and that external causes (such as the movement of the spider while the end of its line is fixed, or when a current of air takes an emitted line and carries it in a direction contrary to that of the spider) also serve to draw the threads out. In all these ways, no doubt, are produced the gossamer lines which often cover the surface of the ground and herbage in autumn. In the formation of their snares spiders use the hinder or fourth pair of legs for drawing the threads tight, and apparently for ascertaining their power of tension. The third, or inferior tarsal claw, being usually strongly bent, no doubt enables spiders to perform these operations very readily. Some large groups of spiders do not spin any snares, and in them we usually find this third claw absent; while in one group, Epeirides, whose snares are marvels of beauty and ingenuity, the third claw is very highly developed. The snares of spiders have been made the basis of some of the primary divisions of the order. Characters, however, taken merely from habits and modes of life, can hardly be considered those on which systematic classification should be based, not to mention that those characters fail when we come to extensive groups spinning no snares at all. Short of such a use of the snares of spiders, this part of the subject is of extreme interest and importance. The Latreillian divisions of snares is fairly and generally accurate; by this method they are divided into Orbitelarice, where the plan is that of a circle or a portion of one, with lines radiating from a centre ; Retitelarioe, where a thin sheet of web is suspended among the branches of shrubs or in angles of buildings, and held up and down by lines in all directions above and below; Tubitelarice, where the snare is a silken tube, inserted in crevices, and fissures, and casual holes, and with an open mouth more or less guarded or armed with insidious Lines ; and Territelarice, in which a tube is spun in a hole formed by the spider itself, and closed sometimes by a close fitting cork-like, or sometimes by a scale-like or wafer lid, some times left open, and at other times closed by the falling over of a portion of the tube which protrudes from the sur face of the ground (see Trapdoor Spiders, by J. T. Moggridge, Lovell Reeve, London, 1873-4). With respect to the econo mic or mercantile value of spider silk, the idea seems to have been entertained, from a remote period, that it might not only be turned to practical use in the manufacture of silk fabrics, but also be made to pay as a mercantile specu lation. The possibility of making it into articles of wear is undoubted, as instances of it are on record. Upwards of 150 years ago Le Bon of France (Languedoc) obtained, from spiders, silk which was afterwards woven into gloves and stockings ; but Reaumur, appointed by the French Academy to investigate the matter, reported unfavour ably, doubting the possibility of rearing the spiders together owing to their voracious and cannibal propensities. In 1777 and 1778 a Spaniard, Raimondo Maria de Termeyer, published, in Italian periodicals, two memoirs on the subject; and afterwards, 1810, at Milan, another called Ricerche e Sperimenti sidla Seta de Ragne, in which he takes an opposite view to that of Re aumur. The latter work is of great rarity (vide B. G. Wilder in Harper s Neio Monthly Mag., xxxiv. p. 455). Termeyer constructed a small kind of stocks, in which the spider was fixed by the body, while with a little winding-machine he drew out and wound up the silk threads from the spider s spinnerets; but evidently nothing came of this further than an additional proof of the possibility of procuring and making use of spider silk, as well as of its strength and lustre; this last, however, as well as other qualities of the silk, would probably be found, as with that of various silk worms, to vary according to the species. Other experiments, with a similar general result, have been made since (Zoologist, 1857, p. 5835), the latest being

those made by Dr B. G. Wilder, professor of anatomy in the