Page:Encyclopædia Britannica, Ninth Edition, v. 2.djvu/308

Rh 288 ARACHNID A [THELYPHOXIDS Araneidea. The palpi in the third family of this order Phrynides bear out this idea strongly. The legs are long, slender, and seven-jointed, except those of the first pair, which have but six, the genual, or fourth, joint being absent. The tarsi of the first pair are divided into eight short articulations, while those of the rest have but three. There is probably some variation in the number of these articulations in different species, since Walckenaer describes the tarsi of the three hinder pairs as five-jointed ; the first pair are far more slender than the rest, palpiform, and without any terminal claw; they appear, as it were, to be thrust out of their position by the great size of the maxillae, and their basal joints seem to be jammed in over those of the second pair. The tarsi of the three hinder pairs terminate with three claws, of which those of the superior pair are the strongest and curved. The abdomen is of a long-oval form, composed of nine quasi segments, formed by a covering, both above and below, of so many transverse articulated corneous plates; while the cartilaginous membrane on each side, between the lateral margins of the upper and lower plates, is continuous, not folded or articulate as in the Scorpionidea. This is a point to be noted, as it marks a transition to the abdominal type of the Araneidea. The first plate on the upper side forms a protective covering to the pedicle by which the abdomen is united to the ccphalo-thorax, and makes the pedicle look broader than it really is. There is a double longitudinal row of impressed circular spots on the upper side, two (in a transverse line) on each corneous plate, except the first and last ; these impressed spots are perhaps points of attachment for muscular fibres. Beneath the abdomen, on the fourth and three following segmental plates, are eight stigmata in as many largish, shallow, circular impressions; they are, however, imperf or ate, and are probably, like those mentioned above, points for the attachment of muscles. The spiracular stigmata are four in number, two being placed beneath the hinder margin of e.ich of the first and second sub-abdominal plates, one on each side of the median line ; the genital aperture is under the hinder margin of the first plate, between the first two spiracular openings. Joined to the posterior extre mity of the abdomen are three small cylindrical, post- abdominal segments, to which is attached a long setiform tail, variable in length, composed of a number of small articulations, and, like the legs and palpi, sparingly fur nished with hairs ; at the extremity of the third post-abdo minal segment, beneath the tail, is the anal opening. The eyes are eight in number : two placed transversely, near to each other, on the fore margin of the caput in the medial line, and three others in a triangular group on each side at its lateral angles, just above the insertion of the legs of the first pair. With regard to the INTERNAL STRUCTURE of the Thely- phonids but little appears to have been ascertained. The respiration is pulmo-branchial ; the spiracular apertures being, as above stated, four in number, and situated in the position already mentioned. Their mode of reproduction is probably like that of the scorpions, ovo-viviparous, but this is conjecture only. GENERAL OBSERVATIONS. The family Thelyphonides is exceedingly homogeneous, and comprises but a single genus, Tkelyphonus (Latr.), of which twenty-nine species only have been recorded and described, twenty-six in one of the latest works upon them, by A. G. Butler, Ann. and May. N. II. 1872, vol. x. pp. 200-206, and Cistula Ento- nwlo-jica, 1873, part vi. pp. 129-132 ; and three others in a still more lecent paper by the late Dr Stoliczka, Journ. As. Soc. Beng., part ii. No. 2, pi. xii. All the species of this small but remarkable group are confined to the tropical regions of Asia, America, and Australasia, no species having yet been recorded from Africa. In size they vary from rather more than half an inch to 2 or 3 inches in length. Among other characters useful ia the identification of the species, are the number and dif ferential development of the various processes and denticu- lations of the palpal joints. Of their habits little if. known, and much of that little is of a very recent date. Dr Stoliczka (I.e.) gives a short account of them, from which it appears that they are nocturnal or crepuscular, living by day in damp places under the bark of old trees ; when disturbed they hold up the palpi, as if for defence, and beat a rapid retreat, with the tail in an erect position. In this position of the tail we see a curious relationship to the scorpions, but apparently without the same necessity, in the present instance, for such a position. They lie still when uncovered, evidently simulating (though of course unconsciously) a fragment of old bark or fungus. The first pair of legs act more as feelers than as organs of locomo tion. In the presence of a sternal plate, the mode in which the abdomen is united to the cephalo-thorax, and the struc ture of the falces, Thelyphonids approach nearer than the scorpions to the structure of the true spiders, and, as we shall see, the family Phrynides is a transitional group bridging over some part of the gap between the two, while iu the massive palpi (though imperfectly didactyle), and in some other respects, they show an unmistakable alliance to the scorpions. Family II. Tartarides. This family is nearly allied to the former Thelypho nides but has a more elongated form. The cephalo- thorax is beak-like in front, and is also divided into two parts or segments ; the first comprises the caput, and tha coalesced thoracic segments belonging to the first two pairs of legs ; the hinder part is the smallest, and comprises the second thoracic segments belonging to the third and fourth pairs, but no grooves or indentations mark the union of the segments, its surface being smooth and glossy. The abdomen is united to the cephalo-thorax by a stout pedicle, and is covered above and below, as in Thelyphonides, with eight or nine transverse, corneous, articulated plates, the upper series separated from the lower by a narrow divisional space, covered with a continuous cartilaginous integument. Beneath the fore part, at the hinder margin of the first sub-abdominal segment, a line-like fissure in the median line probably represents the opening to the reproductive organs ; near the fore margin of each of the fourth, fifth, and sixth plates, in a transverse line, are two small elongated stigmata, thought at first to belong to the respiratory apparatus, but further examination seems to prove them to be, like the eight analogous stigmata in Thelyphonides, imperf orate, and probably due to the same cause conjectured in regard to them. Two (or four) narrow- slits, placed two and two symmetrically on each side of the genital aperture at the fore margin of the first and second segments, but very difficult to be correctly ascer tained, are probably the external openings to the respiratory organs ; these points, however, can hardly yet be said to- be satisfactorily determined. Two or three very narrow corneous rings, or post-abdominal articulations, support a caudal appendage, either slender, cylindrical, and bi-arti- culate, or of a largish, peculiar, sub-triangular form r articulated to a small foot-stalk. Eyes none, no traces even of eyes being visible. The falces are strong, of a flattened cylindrical form, deeper than broad, projecting in the plane of the cephalo-thorax, and terminating with a sharp, curved, movable fang at their upper extremity, the lower extremity being rather pointedly prominent. The palpi are very strong, five-jointed, and each issues from a long, strong, nearly cylindrical basal joint or