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 and hind-guts. The generative organs in the female are very simple, and much like those of the Diplopoda. In the male they are highly complex, and unlike those of any known Arthropod in certain particulars. The wide, unpaired ovary extends nearly to the posterior end of the body. Anteriorly it passes into an oviduct which is unpaired throughout its length. The posterior portion of the duct is wide. The anterior, an abruptly narrowed tube, curves round the nerve-cord and opens by a single sub-median orifice in the third segment. Just within the orifice there opens into the oviduct the short duct of a spherical receptaculum seminis. In the male the testis is never paired. Sometimes it is single, sometimes divided into an anterior and a posterior mass, and sometimes merely constricted. It lies above the intestine in the posterior half of the body in the adult, but at least in the young in some cases, where as many as four divisions have been detected, its position is more lateral. Leading from the sperm masses there may be as many as three slender short ducts which soon expand into wider tubes. These tubes, regarded as seminal vesicles, after forming a complex of loops, coils and caecal prolongations, ultimately unite beneath the intestine in a single tube which passing forwards divides on each side of the alimentary canal to terminate in the two penes situated just behind the bases of the second pair of complete legs, that is to say, the legs of the third segment. Just at the root of the penis there is an accessory gland on the duct, and a little farther back a much larger glandular swelling.

The Pauropoda are divided into three rather sharply defined groups or families which may be briefly characterized as follows:—

Pauropodidae.—Head not covered by the first tergal plate. Anal segment not covered by the sixth tergal plate. Terga of the first ten body segments fused in couples. Tactile setae situated on the lateral portions of the terga which are neither sculptured nor spinous. (Pauropus, Stylopauropus.)

Brachypauropodidae.—Head and anal segment free and the terga smooth as in the last; but each of the double terga of the Pauropodidae divided into an anterior and posterior plate by a transverse band of membrane and each of these into a pair of plates by a longitudinal integumental strip. The tactile setae arising from the pleural area of the segments. (Brachypauropus.)

Eurypauropodidae.—Body wide and onisciform, the head and the anal segment concealed dorsally by the first and penultimate terga respectively. Terga fused as in the Pauropodidae, but thickly spinous or sculptured. The tactile setae situated beyond the edge of the terga, as in the Brachypauropodidae. (Eurypauropus.)

The genus Pauropus is probably world-wide in distribution, since it has been discovered in Europe, North and South America, and in Siam. The two known species of Brachypauropus were found respectively in Italy and Austria. Eurypauropus has representatives in North America and Europe. Examples of Pauropus are extremely agile, recalling the centipede Lithobius in their movements; those of Eurypauropus, on the contrary, are extremely slow and quite comparable in lack of agility to the common pill-millipede. They are usually found in woods, under stones, fallen branches, dead leaves or other damp situations. They are believed to be vegetable feeders and are oviparous. The young upon hatching has four segments and three pairs of legs representing the first three pairs of ambulatory legs of the adult. The two last segments are apodous, the first bears the first pair of legs, and the second the second and third pairs. The young passes through four successive moults, and gradually acquires its full complement of segments and limbs.

CLASS SYMPHYLA. Prosogoneate Arthropods, differing in many important particulars from the Diplopoda and Pauropoda. The axis of the head lies in the same straight line as that of the body, as in the Chilopoda, and not at right angles to it as in the Diplopoda and Pauropoda. There are no eyes. The antennae are very long and many-jointed. Four pairs of gnathites attached to the under-side of the head have been detected. The first pair (mandibles) are two-jointed, as in many Diplopods. The second pair (maxillulae) are minute, one jointed and articulated to a median lobe or hypopharynx which is supported by two chitinous skeletal rods. The third pair (maxillae) consist of a long, basal segment terminating distally in two lobes; near the distal end of the basal segments there is externally a minute one- or two-jointed process, regarded as a palpus. Between the maxillae lies a large, double plate (labium or maxillae of second pair) which is attached proximally to two rod-like basal segments and terminates distally in two pairs of short lobes. The body is long and narrow and bears on its dorsal side fifteen tergal plates. The first of these, immediately succeeding the head, is very short; the remainder are large and sub-equal in size. The adult animal is furnished with twelve pairs of walking legs, which, with the exception of the first pair, are alike in size and segmentation. Each consists of five segments, the distal of which is long and terminates with two powerful claws. The proximal segment bears internally a slender, cylindrical process which may be termed the parapod. It has been asserted that the segment bearing this parapod is in reality the second and that the true basal segment or coxa is embedded in the ventral integument. The legs of the first and second pairs never have the parapod, but they are invariably present in the remaining ten pairs. The legs of the first pair are never more than four-jointed; they are always smaller than the others, and are sometimes reduced to mere bud-like processes. They belong to the first segment behind the head. The segment represented by the last tergal plate has no ambulatory limbs; but articulated to its posterior border is a pair of large, backwardly directed sclerites, which are perforated by the ducts of two spinning glands. These segments are regarded by some authors as the appendages of the last segment, and have been compared to the cercopods of insects. Attached also to the sides of the last segment in front of the spinning mamilla there is a sub-conical papilla bearing an apical seta arising from a cuplike depression. It has been suggested that these papillae also represent a pair of appendages. In that case the last segment must be double and bear two pairs of appendages. Thus there may be as many as fourteen pairs of trunk appendages. There are, however, only twelve pairs known to exist with certainty. These are represented by as many segments on the ventral side; but are numerically less by two than the terga. It is not known whether this very unusual phenomenon is to be accounted for by the addition of two supernumerary terga or by the excalation of two pairs of appendages. The legs of the first pair are basally in contact; the rest are separated by a triangular sternal area. At the base of the legs, with the exception of those of the first and last pair, there, is a slit-like orifice recalling the coxal sacs of certain Diplopoda (e.g. Lysiopetalum, Platydesmus). In internal anatomy the Symphyla closely resemble the Diplopoda. The alimentary canal is straight and simple, with a pair of "salivary" glands opening into the fore-gut, and a pair of malpighian tubes joining the hind-gut close to its communication with the mid-gut. There is a dorsal heart with segmental ostia and valves, and also a supraneural vessel. The silk glands, which occur in both sexes, are situated as in Lysiopetalum. The generative glands and ducts, which are paired, lie between the alimentary canal above and the normally constructed nerve-cord below, and are accompanied in the male by a pair of seminal vesicles; and the orifice lies ventrally in the third segment behind the head. A peculiarity in which the Symphyla differ from all “tracheate” arthropoda is the presence of a single pair of tracheal tubes opening by a pair of spiracles on the lower surface of the head behind the antennae.

The newly hatched young has a smaller number of appendages than the adult, the full complement of legs being reached only after successive moults.

The known species of Symphyla are referred to two genera, Scolopendrella and Scutigerella, which together constitute the family Scolopendrellidae. The chief difference between the two lies in the form of the tergal plates, which in Scolopendrella have the posterior