Page:Popular Science Monthly Volume 9.djvu/598

572 exists no longer in the adult organism, it is present only in the embryonic. It is supplanted by that of the blood proper. Coincidentally with the 'joint' at the frontier of the articulate sub-kingdom there occurs a heart to circulate the blood, fibrine, and with it an order of floating corpuscles more highly organized in the fluids; a wondrous development of the muscular apparatus, striæ in the muscle-cell, a rapid increase in the dimensions of the cephalic ganglia, and in those of the organs of the special senses. It is here in the history of the reproductive system that the diœcious character is first unquestionably assumed. These are noteworthy events in the ascensive march of organic architecture."—( Magazine of Natural History, 1854.)

The armor-plates of the cylindrical Iulus are composed of a semicrustaceous hard substance, but in the Scolopendridœ, which our "false wire-worm" closely approaches, the integuments are of a flexible chitinous substance, the back of each segment is covered by a plate, the ventral surface by a somewhat smaller plate, the epimeral portions, as well as the interspaces between the somites, are covered by a loosely-fitting coriaceous membrane of much thinner texture.

The circulating system has been a battle-ground for men with great reputations. The nervous and reproductive systems, and the development day by day from the ovum, have been drawn out with elaborate minuteness by Newport, in "Philosophical Transactions" for 1841 and 1843, but I have not fallen in with a drawing of their tracheary system, which is well worthy of careful study.

The spiracular orifices are not placed as in insects between the segments, but in the side of each, a little below the dorsal plate; they are not minute apertures, nor vertical slits, neither are they furnished with "guards" of setæ, or hairs, to exclude dust and foreign bodies; but they are circular openings, each with a well-defined, hard-looking ring, over which the tough but pliable lateral membrane passes, lining the entrance, which is directed slightly backward, and can be closed by a sphincter-muscle. The tracheæ are very large in the anterior segments, occupying no small portion of their internal cavities, but they decrease in diameter in proportion as the segments recede from the head; possibly there may be need for a more abundant supply of oxygen in the region of the brain, and in the first-formed portions of the body, than in the equally large but more remote additions which are from time to time developed near the caudal extremity.

Let us detach half a dozen pairs of spiracles, with their tracheal appurtenances complete, from the dissected tail-end of Geophilus the much maligned, float them on to a slide, and bring the "two-thirds objective" to bear upon them.

A ladder of shining silver, a very Jacob's ladder, bright and beautiful enough to have been let down from heaven for the feet of angels.

The six uprights and the cross-rungs are all constructed of the same tubular wire rope glistening with a dazzling metallic lustre, and