Page:EB1911 - Volume 18.djvu/497

 are questions to which no answer can as yet be given. judging from the segmentation and the appendages the body is composed of twelve somites, including the last or anal, which, like the penultimate somite, is limbless. Each somite in front of the penultimate bears a single pair of legs, nine pairs of which are fully developed ambulatory limbs, while those of the first segment are reduced to a pair of bud-like processes.



—Enlarged view of Pauropus huxleyi, from ventral side. The first and last pairs of ambulatory limbs consist of five segments; in the remaining pairs the terminal segment may be subdivided into two, so that there may be six segments in all. The ambulatory limbs are usually terminated by three claws, a principal and two subsidiary, each claw being accompanied by a membranous pad. Between these limbs, which are relatively longer and stronger than in the Diplopoda and evenly spaced on each side of the body, extends a soft-skinned sternal area. The distensible pleural region of the body is also membranous, but the dorsal area is covered by chitinous plates or terga, usually six in number, excluding that of the anal segment; each of the anterior five of these overlies two limb-bearing somites, the first covering the somite of the rudimentary limbs and of the first pair of locomotor legs, the second those of the second and third pairs of locomotor legs, and so on. This condition is an adumbration of the far completer fusion of somites seen in the Diplopoda. The sixth tergal plate belongs to the limbless penultimate somite. The duplex character of the first five terga is suggested in Pauropus by the presence of two rows of sensory bristles; there being only one such row upon the sixth tergum. In the aberrant genus Brachypauropus the evidence is practically completed by the correspondence in number between the terga and pairs of legs, there being a divisional line between the two rows of setae. On each side of the body there are five long pubescent tactile setae situated on the second to the sixth terga in Pauropus, and on the pleural area corresponding to these terga in Brachypauropus.

The cerebral mass of the nervous system is large and when viewed from above is seen to consist of two lobes defined by a median groove. In the absence of eyes no optic nerves are given off. Beneath these are two antennal lobes whence arise, close together, the antennal nerves. Two short commissural cords connect the cerebral mass with the suboesophageal ganglion, a composite mass formed of the nervous centres which supply the two pairs of jaws and the rudimentary legs of the first pair. Behind this large ganglion the cord, which shows superficially no trace of its double origin, presents a ganglionic swelling for each pair of legs. No circulatory or respiratory organs have been detected.

After Kenyon, Tufts Coll. Studies, iv., 1895.


 * A. Alimentary canal of Pauropus; fg, fore-gut; sg, salivary gland; mg, mid-gut; hg, anterior portion of hind-gut; a, anus; m.p.t., malpighian tubule.
 * B. Female genital organs of Eurypauropus; ov, ovary; ovid, oviduct; rs, receptaculum seminis; go, genital orifice.
 * C. Male genital organs of Pauropus; t1 and t2, anterior and posterior portions of testes; vd1, vd2, vd3, vasa deferentia; vs.s, vesicula seminalis; cd, common duct; go, genital orifices.
 * D. Lateral view of Pauropus; c, head; ant. antenna; tg1, tg5, first and fifth tergal plates; a.sg, anal segment; st, lateral bristles; lg.r, rudimentary leg; lg1 and lg9, first and ninth fully formed walking legs; p, penis.

The alimentary canal consists of a short, narrow fore-gut, a large, straight mid-gut, and a moderately long hind-gut which is itself composed of two parts, an anterior narrow tube which opens into a dilated, piriform, posterior portion, narrowing gradually to terminate in the anus. Opening into the anterior extremity of the fore-gut there is a pair of “salivary” glands. Malpighian tubes have been found in some forms, i.e. females of Eurypauropus spinosus, but not in any examples, male or female, of Pauropus huxleyi. Where present they open at the point of union of the mid-