All these functions are performed by the silk-glands of the Orb-weavers, and hence it is with them that the organs have attained their greatest perfection. We may conveniently take the case of the common large Garden-spider, _Epeira diademata_. The glands occupy the entire floor of the abdomen. They have been very thoroughly investigated by Apstein,[266] and may be divided into five kinds. [Illustration: FIG. 187.—Spinning glands. =A=, Aciniform; =B=, tubuliform; =C=, piriform gland. ] On either side of the abdomen there are two large “ampullaceal” glands debouching on “spigots,” one on the anterior, and one on the middle spinneret; there are three large “aggregate” glands which all terminate on spigots on the posterior spinneret; and three “tubuliform” glands, two of which have their orifices on the posterior, and one on the middle spinneret. Thus, in the entire abdomen there are sixteen large glands, terminating in the large fusulae known as spigots. In addition to this there are about 200 “piriform” glands whose openings are on the short conical fusulae of the posterior and anterior spinnerets, and about 400 “aciniform” glands which debouch, by cylindrical fusulae, on the middle and posterior spinnerets. Thus there are, in all, about 600 glands with their separate fusulae in the case of _Epeira diademata_. The great number of orifices from which silk may be emitted has given rise to the widespread belief that, fine as the Spider’s line is, it is woven of hundreds of strands. This is an entire misconception, as we shall have occasion to show when we deal with the various spinning operations. A few families are, as has already been stated, characterised by the possession of an extra spinning organ, the cribellum, and the orifices on this sieve-like plate lead to a large number of small glands, the “cribellum glands.” =Respiratory Organs.=—Spiders possess two kinds of breathing organs, very different in form, though essentially much alike. They are called respectively “lung-books” and “tracheae.” The Theraphosae (and _Hypochilus_) have four lung-books, while all other spiders, except _Nops_, have two. Tracheae appear to be present almost universally, but they have not been found in the Pholcidae. The pulmonary stigmata lead into chambers which extend forwards, and which are practically filled with horizontal shelves, so to speak, attached at the front and sides, but having their posterior edges free. These shelves are the leaves of the lung-book. Each leaf is hollow, and its cavity is continuous, anteriorly and laterally, with the blood-sinus into which the blood from the various parts of the Spider’s body is poured.