line—and thus can rapidly escape from the side of his mistress, who, after receiving his caresses, has an unpleasant habit of seizing, killing, and sucking the blood of the adventurous male, should he linger longer in her company, and fail in the agility and rapidity of his exit. [Illustration: FIG. 49.—Section through the body of a spider to show the spinning organs. _h_, heart connected by four big veins with _b_, the lung-bosks or air-gills; _f_, genital lid; _ov_, ovary; _a_, the anus; _spn_, the three pairs of spinnerets or spinning warts; _c_, _e_, and _d_, the three kinds of glands producing liquid silk, viz., cylindrical, tree-form, and pyriform. These are one thousand in number in the common garden spider, and each has its separate spout or spigot standing up on one of the spinnerets (see next figure).] [Illustration: FIG. 50.—One of the two middle spinnerets of the common garden spider (_Epeira diadema_), to show the three kinds of spouts or spigots (one thousand in all) corresponding to the three kinds of silk-glands. Each kind of “spigot” pours out a different kind and size of thread. _sp.c_, one of the big spigots of the cylindrical glands; _sp.t_, middle-sized spigots belonging to the tree-form glands; _ss_ and _s.ss_, the small-sized spigots of the very numerous pyriform glands.] The threads of the garden spider (the _Porte-croix_ of the French, white-cross spider, _Epeira diadema_, Fig. 51) are fixed by astronomers in their telescopes for the purpose of giving fine lines in the field of view, by which the relative positions of stars may be accurately measured. For a century astronomers desired to make use of such lines of the greatest possible fineness, and procured at first silver wire drawn out to the extreme limit of tenuity attainable with that metal. They also tried hairs (1/500th of an inch thick) and threads of a silk-worm’s cocoon, which are split into two component threads each only 1/2000th of an inch thick. But in 1820 an English instrument maker named Troughton introduced the spider’s line. This can be readily obtained three or four times smaller in breadth than the silk-worm’s thread, and has also advantages in its strength and freedom from twist. In order to obtain the thread, the spider is carefully fixed on a miniature “rack,” and the thread, which at the moment of issue from the body is a viscid liquid, is made to adhere to a winder, by turning which the desired length of firm but elastic thread can be procured. It has been proposed to use spiders’ silk in manufactures as a substitute for silk-worms’ silk, and pioneers have woven gloves, stockings, and other articles from it. It appears that there are species of spider in other parts of the world whose thread is coarser and more suitable for this purpose than that of any of our British spiders. But it is estimated that the expense in feeding the spiders—which require insect food—would make the thread