The Structure and Habits of Spiders

by J. H. Emerton

Fig. 47.

In most spiders the terminal joint is flattened, and has a hollow on the under side, in which the palpal organ is partly concealed. The bulb is flattened to fit this hollow; and the point of it is prolonged into a distinct tube of various shapes, furnished with numerous spines and appendages. [Fig. 47] is the palpal organ of Epeira vulgaris flattened out, and made transparent. The internal sac is shown at a; and the tube from it b runs round the inside of the bulb, and ends at the opening c. The outside of the organ has various horns and appendages. [Fig. 48] is the palpus of another spider, where the outer tube is so long, that it is coiled up over the basal part of the bulb; and the end rests on a strong spine at one side of the palpus.

Fig. 48.

Not only the terminal joints of the palpi, but also the next, and sometimes next two joints, are modified in shape, with the development of the palpal organ, [Fig. 48]. The shape of these organs is very constant in the same species of spider, and thus becomes one of the most convenient marks of such a group.

THE EPIGYNUM.

When the female spider is nearly full grown, there appears a hard, swollen place just in front of the opening of the ovaries, [Fig. 1]; and, after the last moult, the epigynum is uncovered at this place. The epigynum, [Fig. 49], consists of two spermathecæ, E, which connect by two little tubes, H, H, with the oviduct near its mouth, and by two larger tubes, D, with the outside of the spider. The mouths of these larger tubes are often surrounded by various hard appendages to support and guide the palpal organs when the latter are thrust into them. These parts, like the palpal organs, furnish convenient marks for distinguishing species. The spermathecæ, E, vary but little in shape in different spiders; but the tubes H and D are often lengthened, and twisted into shapes nearly as complicated as those of the palpal organs. [Fig. 50] is the epigynum of a small Theridion, where the arrangement of parts can be very distinctly seen. E, E, are the spermathecæ; H, H, the tubes opening into the oviduct; and D, D, the tubes opening outward. [Fig. 51] is the epigynum of another closely allied species, where the tubes D, D, are very much elongated and twisted up, corresponding to the long discharge-tube of the palpal organ of the male of the same spider, Fig. 48.