Page:Encyclopædia Britannica, Ninth Edition, v. 2.djvu/303

SCORPIONS.] AEACHNIDA 283 labium, and differs in its form in different species. The eyes, two or four in number, are situated on each side of the fore part of the cephalo-thorax, but there are none in the medial line. In some instances eyes are wanting alto gether. With regard to internal structure, the Pseudo-Scorpi- ones are very similar in their muscular system to the spiders (Araneidea) (Menge). The digestive apparatus is simple ; a large stomachal pouch contracted a little in the middle lies in the thoracic cavity, and from it the alimentary canal runs through to the hinder extremity of the abdomen, with a double crook in the course of its passage ; this canal is imbedded on all sides in a mass of substance serving the function of a liver. The external spinning organs have already been mentioned ; the internal apparatus resembles that of spiders, consisting of a number of small elongated pear-shaped sacs, communicating outwardly with the spinning tubes. Nothing certain appears to have been discovered in regard to the circulatory system of the pseudo-scorpiones, except that a simple vessel runs along beneath the middle of the abdominal ridge ; the vital fluid being found free among all the other organs of the body, so that the air is conveyed to the blood by numerous air-tubes, and not the blood to the air. The tracheal character of the respiratory system has been just mentioned. The spiracular openings vary in number in different species, two or four. From the two hindermost of the abdominal apertures, when four are present, there issue more or less numerous thread-like tubes, which convey the air to the different parts of the abdomen. From each of the two foremost stigmata a main tube runs obliquely through the thoracic region, and from this tube finer ones issue to the rest of the cephalo-thorax and its adjacent parts legs, palpi, and falces. When two spiracular open ings only are present a large tube runs from each forwards into the thorax, and finer ones backwards into the abdominal parts. The reproductive organs are simple. The external parts in both sexes are situated in the second (?) segment be neath the fore part of the abdomen, and consist of two small oval openings close together. Into each of these there opens in the male a curved horn-like sac, with a lateral direction, as well as a smaller longitudinal duct, the latter leading from a common seminal receptacle. In the female a two-branched oviduct leads from the ovaria into the external apertures ; the mode of reproduction is ovi parous, and the eggs are carried by the female beneath the fore part of the abdomen, somewhat like those of certain of the Araneidea. GENERAL OBSERVATIONS. The Pseudo-Scorpiones are all of very small size ; they do not appear to form more than one family group, Pseudo-Scorpionides, of which several genera and numerous species have been described by various authors. They are widely distributed, being found in tropical as well as in temperate climates. Europe possesses many species, and even England has several these being the sole representatives of the Scorpionidea in this more northern latitude. Their habitat is under stones, beneath the decaying bark of trees, on the damp soil, among moss and herbage ; some are found amongst old papers in houses, and in herbaria, and others are said to be parasitic on the common house-fly. For more minute details of structure and other particulars, see A. Menge, Ueber die Scheerespinnen, Chemetidce, who separates them from the scorpions under the above name, as a family group, more nearly allied by their internal structure to the true spiders than to the former. Menge gives also a list of works on this sub-order. A paper lately published by Dr Ludwig Koch, at Nuremberg, 1873, pp. 68, describes and gives analytical tables of all the European genera and species at present known. Sub-Order II. Scorpionidea. Between the solpugids and the scorpions (figs. 19, 20) the last group (Pseudo-Scorpiones) gives us an evident connect ing link. In the present sub-order, Scorpionidea, or true ecorpi- Fio. 19. Scorpion (Buthus heros, Koch), a, a, palpi, of which A, h, are (he digital or fourth joints, and i, i, the movable fingers; 6, 6, falces, with two movaUo fangs, k, *, and two fixed ones, **, i*- rf, eyes; e...e, tipper segmental plates of abdomen ; /.../, articulated cartilaginous membrane, connecting upper and under plates of abdomen ; m, bulbous sting. ons, the EXTERNAL STRUCTURE consists of a more or less elongated-oval body, covered with a coriaceous, or hard and Fio 20 Scorpio Amoreiixii, Sav., under side, with legs, palpt, and falces truncated, a, a, maxilla;; i, ft, supernumerary or second pair of maxilla:, supporting first pair of legs; c, <-, third pair of ditto supporting second pair of legs- <?...<*, basal joints of two hinder pairs of lees; / orifice of sexual organs- A, !>, comb-like appendages (also figured i-cpnrattly, enlarged) j i...i, eight spiracles leading to breathing organs; *, rudimentary sternal plate; o, >, portion of third pair of supernumerary maxillic acting as a sternal labium. horny integument. The cephalo-thorax is tuberculate or granulose, and marked with various seams, or grooves, and ridges, no doubt indicating the union of the caput and

tho racic segments. One longitudinal, and, in general, strongly