168 NATURAL HISTORY. 



after a time into two main branches, and sends forth a great number of arteries to the organs of 

 the cephalothorax and the limbs. Respiration is effected, as already mentioned, partly by lung-sacs 

 and partly by tracheae. The former, of which there are one or two pairs, are situated in the basal part 

 of the abdomen, where they open by slit-like stigmata protected by small special plates (opercula). 

 Their structure and mode of action are the same as already described in the Scorpion. The trachea? 

 consist of two main stems, with more or less numerous branches, sometimes possessing more or less 

 distinct internal fibres, sometimes partially or wholly destitute of anything of the kind. The main 

 stems open to the air by a pair of stigmata situated in the lower surface of the abdomen, sometimes 

 close to those of the lung-sacs, sometimes at the extremity of the body. The aperture of the 

 generative organs is placed in both sexes at the base of the abdomen, between the stigmatic 

 openings. The central nervous system is much more concentrated than in the Arthrogastra, con- 

 sisting only of a central or supraoesophageal ganglion and a great nervous mass behind the 

 cesophagus, the latter showing on each side four projecting portions, from which the nerves of the 

 limbs are given off. 



Besides these internal organs, the Spiders universally possess a set of glands for the production of 

 a viscous fluid which has the property of hardening upon exposure to the air, and forms the silky 

 threads which play so important a part in the lives of thesa animals. Thesa silk-producing glands 

 are exceedingly numerous, and pour out their secretion through a multitude of minute tubes situated 

 on the lower surface of a set of peculiar organs known as spinnerets, placed near the extremity of the 

 lower surface of the abdomen. There are from two to four pairs of these organs, which are sometimes 

 quite short and nipple-like, placed close together in a little bunch, while sometimes one or two pairs 

 are more elongated, and even divided into joints. In the latter case it is only the apical joint that 

 bears the spinning tubes or " spinnerules " on its lower surface. The latter consist of microscopic 

 horny tubes, through the minute apertures at the extremity of which the silky secretion escapes in 

 threads of extreme fineness, a number of which unite before their consolidation to form the threads 

 with which we are familiar. The production of these silky threads is, indeed, the most striking 

 characteristic of the Araneida, and it enters more or less importantly into all their habits of life. By 

 means of it they construct their dwellings, and some of them make most ingenious nets for the capture 

 of prey ; they make use of it continually when prowling about, as a safeguard against falling ; they 

 employ it in the construction of bridges, to cross from one elevated situation to another, and even as 

 a means of aerial transport. The two last-namel uses of the silky material require a few words of 

 explanation here, as they are common to Spiders of several families. For the formation of a bridge 

 from one tree, or other elevated object, to another, the Spider places itself on the summit of its resting- 

 place with its front to the wind, and clings firmly to its support, usually with the aid of a few short 

 threads stretched transversely to the direction in which it is looking. It then attaches a thread to 

 the surface on which it is standing, and elevates the extremity of its abdomen as much as is possible. 

 The wind immediately catches the short thread thus produced and exposed to its action, and draws it 

 out continually, forming a loop of gradually increasing length, which floats away until it comes into 

 contact with some solid body, to which it clings. The Spider has then only to draw the line tight and 

 fasten it, and his communication with the distant point is complete. The same process is adopted with 

 a view to an aerial excursion, a mode of diversion to which young Spiders of several families are very 

 much addicted especially in the fine days of autumn. In this case, however, when the Spider feels 

 that the quantity of silk that it has produced is sufficient to enable the aerial currents to bear it up 

 into the air, it cuts away the original attachment of the thread and allows itself to be carried off.* 

 Sometimes these flying threads are excessively numerous, and on their descent cover everything ; 

 they are particularly striking on hedges, and constitute, at all events, one of the causes of the pheno- 

 menon well known in the country as "gossamer." 



The Spiders are all oviparous, and it would appear that the female, when once impregnated, pro- 

 duces several batches of eggs at considerable intervals of time. The number of eggs produced at once 

 varies, but they generally form a considerable mass, enclosed by the female in a silken bag, which 

 she sometimes carries about with her, sometimes conceals in her nest, and sometimes attaches to 



* According to many writers no preliminary attachment of the thread takes place, but the Spider simply emits some 

 fluid from the spinnerets, and allows the air to cany it away. 



