Page:Encyclopædia Britannica, Ninth Edition, v. 2.djvu/310

Rh 290 ARACHNIDA [SPIDERS. and tenuity, the three terminal joints forming one long slen der tapering portion, which is however subdivided into a great number of minute homogeneous articulations without any terminal claw ; each tarsus of the remaining three pairs is divided into three articulations, ending with two curved claws ; and in some species the tibial joint of the fourth pair is also tri-articulate. Probably the subdivision of the fourth pair of legs varies in other species also. The coxal joints of the first pair are, as it were, crushed in behind the maxillae and above the coxse of the second pair, as in Thelyphonus. The extreme articulation of each tarsus has a peculiarity never (it is believed) noticed before ; its upper side being covered, throughout its length, with a sepa rate integumental plate, prolonged at its fore extremity into a corneous, slightly bent, claw-like apophysis, forming a kind of third claw above and between the two ordinary ones. These latter spring from a supernumerary or heel joint, which has a short, conical, tooth-like spur beneath it, representing the usual third claw in other groups. The eyes, eight in number, are placed in three groups, forming a very obtuse angled triangle on the fore margin of the caput. Two eyes, seated transversely, and near together in the medial line, constitute the apex of the triangle, which is directed forwards ; the other two groups are of three eyes each, closely grouped in a triangular form, one on each side, about parallel with the second pair of legs. The abdomen is oval, of a somewhat flattened form, and joined to the cephalo-thorax by a narrow pedicle, showing, in this also, a near approach to the Araneidea; it consists of ten quasi-segments, or articulations, formed, as in the other families of the order, by a series of upper and lower transverse corneous plates, having an, apparently continuous, cartilaginous integument between the two series of plates, and terminating with a button-like joint, or process, at its extremity. On the under side are two parallel rows of impressed spots, two, in a transverse line, in each of the fourth and three following sub-abdominal plates; but, apparently, like the corresponding marks in Thelyphonus, imperforate. The organs of generation have their exter nal orifice beneath the posterior margin of the first sub- abdominal plate; and the external openings to the re spiratory organs, four in number, are situated, two beneath the posterior margin of the first, and two others beneath that of the second of these plates. The sternum is oval, and often superficially divided into several portions by various ridges and indentations. With regard to the INTERNAL STRUCTURE of the Phry- nides, the respiratory system is pulmo-branchial, the orifices to these organs being four in number, and placed as above mentioned. The nervous system, according to Van der Hoeven, appears to be very simple, consisting of a large thoracic bi-lobed ganglion, from which four pairs of lateral nerves issue, while a double nervous chord runs back through the connecting pedicle into the abdomen, where it divides into two divergent branches, from which the various nerves are distributed to the different parts of the abdomen. GENERAL REMARKS. The family Phrynides comprises but one genus, Phrynus (Olivier), which, according to the most recent publication upon it (A. G. Butler, I.e. supra], includes twenty species only, all confined to the tropical regions of the world. The individuals of most of these species appear to be of rare occurrence, or, at least, but rarely observed, and the family has, comparatively speaking, received but little attention. It is, however, one of great interest and importance, and deserves more elaborate and careful treatment, especially in regard to its habits and internal anatomy, for it undoubtedly forms a plain passage from the Scorpionidea (through Thelyphonus and Nyctalops) to the true spiders (Araneidca). The main external marks of affinity with this order have been noticed in speaking of the different portions of external structure of the Phrynides. Order VII. ARANEIDEA. TVe have come now, by an easy transition from the Phrynides, to the last order of Arachnids Araneidea or True Spiders (figs, 26, 27, 28). And first, with regard to FIG. 26. Spider (Cambridyea fatciata, Koch). Adult male. their EXTERNAL STRUCTURE, they consist, like others of the sub-class Arachnida, of a body divided into two parts cephalo-thorax and abdomen ; but these are united only C Fig. 28. FIG. 27. Cambridgea fasciata ; adult male, under side, with legs and one palpus truncated. /, sternum; g, g, maxillse ; ft, labium; k, k, falces, with* 1 fangs of ditto ; m, one of ordinary spiracular orifiVcs (the corresponding one on opposite side not lettered); n, genital aperture, leading, in the male, only to spermatic vessels ; o, o, spinners ; p, anal orifice ; t, t, extra pair of spiracular openingt ; 1, digital joint of palpus; 2, palpal organs; 3, radial joint; 4 cubital; 5 humeral 6, axillary. FIG. 28. The same upper side of cephalo-thorax. a. ..a, coalesced thoracic seg ments; b, caput; c, c, falces; d, eyes; e, central indentation. by a slender pedicle, and neither is segmented, ringed, or articulated, nor (in respect to the abdomen) covered with