572 THE POPULAR SCIENCE MONTHLY. 



exists no longer in the adult organism, it is present only in the em- 

 bryonic. 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, striae 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 reproduct- 

 ive system that the dioecious character is first unquestionably assumed. 

 These are noteworthy events in the ascensive march of organic archi- 

 tecture." (De. Williams, Magazine of Natural History, 1854.) 



The armor-plates of the cylindrical lulus are composed of a serni- 

 crustaceous hard substance, but in the Seolo])e?idridce, 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 por- 

 tions, 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 develop- 

 ment 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 seg- 

 ments, 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 setae, 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 cau be closed 

 by a sphincter-muscle. The tracheae are very large in the anterior seg- 

 ments, 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 beau- 

 tiful 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 



