Page:Encyclopædia Britannica, Ninth Edition, v. 2.djvu/298

Rh 278 AEACHNIDA [PHALANGIDS. the second joint terminates with a didactyle claw or pair of pincers, formed by a movable claw acting in opposition to a fixed one. The falces vary greatly in their size and development. The terminal joint is sometimes articulated to the basal one at the extremity of its longer axis or at its end ; at other times it is attached by its shorter axis, or more or less near the middle. In some species they are furnished with pro cesses or horny prolongations, differing in size and form in different species ; this is, however, only a modification of the last mentioned mode of articulation. The legs are, in most species, very long and slender; in some groups they are, however, shorter and stronger, while in others they are of extreme length and tenuity. They are eight in number ; the seven normal joints, of which each is composed, may be more properly described as con sisting of five invariable and two variable ones ; the sixth (or metatarsus) being divided into several immovable divi sions, and the seventh (or tarsus) subdivided into a greater or less number of minute movable articulations, the ter minal one furnished with one or two fine claws. The legs are often armed (some, at least, of their joints) with strong spines and spiny processes; this is particularly the case in the family Gonyleptides. The first joint (coxa) of each leg is immovable, being fixed to the side and under part of the cephalo-thorax. Between the fixed (or basal) joints of the legs is an oblong, or at times somewhat obtusely triangular, sternal plate, divided at its base from the abdomen by a transverse groove ; the anterior extremity is free, and beneath it is concealed (according to the sex) the penis of the male, or the ovipositor of the female ; in some species of Phalangides these organs are of great length and varied in form ; this sternal plate forms the lower side of the cephalo-thorax. The eyes, two or eight 1 in number, are generally of large size, and situated on the sides of a common eminence on the upper side of the cephalo-thorax ; this eminence is often armed with spines and tubercles. INTERNAL STRUCTURE. Muscular System. Every one who has seen the mode in which the Phalangides run would naturally suppose that the muscles required to keep the body raised and balanced between their long slender legs in rapid course must be exceedingly strong; and this is found to be the case. The muscles are of large size, consisting of numerous strong &quot;fasciculi,&quot; which arise from the interior of the basal joints (coxa^ of the legs, and, almost entirely filling up their hollows, pass on into the next joint (trochanter), and so on to the end of the second part of the tibia: ; thence two 1 jng delicate tendons, continuing forwards, traverse the whole length of the tarsal joints, running along their under surface. The muscles by which the falces and palpi are worked consist of an elevator and a, somewhat larger, depressor for each. Other muscles and muscular fibres connected Avith other parts and organs are minutely described by A. Tulk, 2 whose descriptions, however, cannot be usefully abridged, and are too extensive and detailed for our present space. Organs of Digestion. These consist of a simple longitudinal pouch forming the stomach or main intestinal canal, contracted at each end, enlarged in the middle, and giving off on all sides numerous lateral pouches or creca of different sizes, to the number, in Phalangium opilio (Latr.), of thirty. These are minutely detailed by Tulk, who divides them into (1), those on the dorsal surface of the inain canal ; (2), those on its ventral surface ; (3), those on its sides. The pharyngeal tube and oesophageal canal are modified so as to be qualified not only for the passage of simple fluids, but also for solid substances ; these first, ;however, having undergone a process of quasi- mastication by means of the external parts of the mouth. At the opposite end of the alimentary canal a simple, short intestine connects it with the anus, the external aperture of which is situated at the hinder extremity of the abdomen. &quot;With regard to the office of the lateral cnsca, an examination of their contents has led to the suggestion that they secrete a peculiar granular substance, which is thence discharged into the stomach, and &quot;agglutinates the particles of food together,&quot; covering them with a membranous integument which serves to protect the delicate coats of the intestine from laceration by the sharp and spiny nature of their food-contents (Tulk, I.e. p. 248). Biliary tubes have been 3 &quot;Upon the Anatomy of Phalangium opilio (Latr.),&quot; Ann. N. H., Nos. 76, 77, and 78, Oct. 1843. described by Treviranus ; but it seems probable that the anterior pair of these, at least, are trachese connected with the stigmata on each side of the fore margin of the cephalo-thorax. These stigmata were mistaken by Tulk for eyes (I.e. p. 156). The Organs of Respiration are tracheal. The stigmata in Phalan gium (and Gonyleptes ?) are four in number, two beneath the foro part of the abdomen, situated one at the base of each of the posterior legs, but usually concealed by the coxal joints, and one on each side of the fore margin of the cephalo-thorax ; each of the former pair opens into a large obliquely longitudinal tracheal trunk ; these two trunks give off various smaller branches and tubes, which convey the air to all parts of the body. With two of these tubes, probably, the cephalic stigmata are connected. The Organs of Circulation are very simple, consisting, in Phalan gium, of an elongated dorsal vessel acting as a heart, lying in a groove upon the upper surface of the alimentary canal, and divided into three chambers. Eamifications from this vessel serve to carry the vital fluid to every portion of the body f Tulk). From researches since made by M. Blanchard, 3 it appears that this fluid is re collected from the general circulation into two large lateral vessels (vascular sinuses), from which it is returned by other channels to the dorsal vessel, or heart itself. The structure of the heart consists of a series of transverse, curved, and muscular bands, leaving between them light and membranous intervals (Tulk). The Nervous System of phalangids is very similar in its type to that of some other arachnids. Two large ganglia (cephalic and thoracic) occupy the cephalo-thorax, and from these nerves issue to the various parts, some of them leaving ganglionic enlargements in their course, whence again finer nerves distribute themselves to the adjacent structures. Tulk mentions a striking peculiarity connected with the nervous system of phalangids, which is a power possessed by them to move the nervous centres backwards or forwards at will ; this is effected by means of several large transversely striated mus cular fasciculi radiating from the sides of the thoracic ganglion, to which they are attached by short tendons (Tulk, I.e. 326). The Organs of Generation in the Phalangidea (which are oviparous), are different from all other arachnids in the large external parts connected with them. In the female, the internal parts consist of an ovisac and ovarium (Tulk) ; whence, by means of the oviduct, the ova arc conducted into the ovipositor. This is a long membranous tube; the first or basal part of it is surrounded by annuli or rings of hairs or bristles; towards the extremity it is scaly, and also furnished with some hairs, and the extreme point has two small lateral tufts of hairs. The ovipositor is protruded, at the will of the animal, from the vulva, which is situated at the fore margin of the sternal plate, or else it is, when at rest, withdrawn into its sheath, leaving no out ward trace of it visible. In the male, the seminal vessels consist of a cluster of &quot; slightly tortuous caical tubes,&quot; whence the spermatic fluid is passed by a duct into a penis of enormous length compared to the size of the animal (fig. 12, d, e, /). This organ is a slender curved tube, furnished at its extremity with a recurved hook, and contained in a sheath ; both the sheath and penis when at rest lie in a longitudinal direction beneath the ventral surface, of the thorax, but can be protruded at will from the external aperture, which is similar, and similarly situated, to that of the female. The form of the penis varies in different species, as also does the ovipositor of the female. The organs of generation, both male and female, of Phalan gium opilio, are detailed a great length by Tulk, I.e. Both tho penis and ovipositor may be made to protrude by, a slight lateral pressure beneath the fore margin of the sternal plate. GENERAL OBSERVATIONS. The Phalangidea have been found in all parts of the world, but though often very numerous in individuals, the number of species as yet discovered is comparatively small. In the British Islands, where about sixteen species have been observed, they are popularly known by the name of &quot; Harvest-men,&quot; 4 pro bably because most numerous at the time of harvest. They run with great rapidity over and among grass and low herbage, and many live among the leaves and mossy covering of trees, among moss on the ground, heath, and stems of herbage; also under stones, and among rubbish and debris. Their prey is small insects, the young of the true spiders, and some species of Acaridea. The small size of the body, compared with the inordinate length of the legs, in some genera is exceedingly striking. In an undescribed species of Leiobunus, from the Brazils, tho length of the body is but a line and a half, while that of 3 &quot; De 1 appareil circulatoiro et des organs de respiration dans les Arachnides,&quot; Ann. Sc. Nat. 3 ser. &quot;Zool.,&quot; xii. 318-352, pis. 6-8. 4 &quot;Monograph on the British Species of Phalangiidseor Harvest-men, by E. H. Mettle, F.L.S., Ann. N. //., June 1855, pp. 393-416.
 * II. 0. Wood, in Trans. Amer. Phil. Soc., xiii. p. 440.