MYRIAPODA. 



549 



overlaps tlie greater number of the pieces 

 belonging to the month. The second segment, 

 by far the larger and the stronger of the two, 

 and, in fact, from the density of its corneous 

 envelope, the strongest segment of the whole 

 body, is entirely devoted to the support and 

 movement of a pair of sharp bi-articulate and 

 hooked fangs resembling jaws, that move trans- 

 versely like the (so-called) mandibles of a 

 Spider, but which are in reality only modifica- 

 tions of the ambulatory feet converted into 

 instruments for killing prey, each being per- 

 forated near its sharp termination with a long 

 oval slit, through which venom is said to be 

 instilled into the wound inflicted by this 

 formidable weapon. 



The head properly so called, namely the 

 circular shield-like plate seen upon the dorsal 

 surface at the anterior extremity of the body, 

 although apparently consisting of a simple 

 horny disc, is doubtless composed of several 

 segments conjoined superiorly ; indeed, these are 

 completely confused, and inferiorly are too soft 

 and membranous to be distinguished, except 

 by the presence of those articulated appendages, 

 which, although forming parts of the mouth, 

 are still merely repetitions of the jointed legs 

 affixed to the other segments of the body. 

 Thus the most superficial plate, with its articu- 

 lated appendage, the lubium and lab ial palpus of 

 entomologists, is but an incomplete ventral 

 scutum, with its articulated limb in a rudimen- 

 tary condition as compared with those of the 

 body, and is even armed with a distinct claw, 

 as are the locomotive legs. In like manner the 

 second pair, the maxilla of authors, are legs 

 but one step further removed from their normal 

 form, but not more so than are the poison- 

 fangs already described. In the third pair or 

 mandibles we have a leg reduced to its terminal 

 claw, and that is broad and serrated so as to 

 become useful in manducation. Lastly, the 

 corneous and serrated piece (the labrum) seems 

 to be the last vestige left of limbs of this 

 description, the two horny remnants of legs 

 having become consolidated with each other 

 and with the dorsal head-plate, so as to form 

 the anterior boundary of the mouth. 



Alimentary canal. The alimentary canal in 

 all the Myriapoda is of extremely simple con- 

 struction, and both in its form and general 

 arrangement, very nearly resembles that of the 

 larvae of Lepidopterous Insects. In Julus ter- 

 restris (Jig. 311) the oesophagus (h) is seen to 

 be of considerable capacity, in accordance with 

 the nature of the coarse food upon which these 

 vegetable-eating species live- The stomach is 

 long and bowel-like, extending from the termi- 

 nation of the oesophagus to the insertion of the 

 hepatic vessels. To this succeeds a wide and 

 sacculated colon, which passes directly to the 

 anal segment of the body, where it terminates. 



In the Scolopendroid genera the same con- 

 formation of the alimentary apparatus is met 

 with, the stomach and intestine passing straight 

 from the mouth to the anus without any pecu- 

 liarities of structure worthy of notice. 



In Lithobius Jbrftcatus, which we may take 

 as a specimen of one of the Chilopod Myria- 



31 J. 



poda, a very similar arrangement exists; the 

 oesophagus, which is pro- 

 portionately narrow, ends 

 in a simple stomachal 

 enlargement of an oblong 

 shape, and this termi- 

 nates in a straight bowel, 

 the point of separation be- 

 tween the one and the 

 other being only indicated 

 by the entrance of the 

 biliary vessels. 



The glands connected 

 with the alimentary ap- 

 paratus closely resemble 

 those of the insect larva. 

 Two convoluted salivary 

 tubes are seen folded up 

 at the sides of the oeso- 

 phagus, where their con- 

 volutions are intervolved 

 into a species of ravel 

 (fig. 311, i) with the 

 origins of the hepatic ves- 

 sels (//), which latter, after 

 a tortuous course, are in- 

 serted, as in Insects, at 

 the termination of the sto- 

 machal portion of the di- 

 gestive tube. 



Respiratory System. 

 The Myriapoda respire in 

 the same manner as In- 

 sects by means of late- 

 ral spiracles and tracheal 

 tubes. The spiracular ori- 

 fices are, in the Scolo- 

 pendridae, very conspi- 

 cuous, as, for example, 

 in Lithobius, (Jig. 312,) 

 where the corneous lips 

 of the apertures leading 

 to the tracheae (.<, s, s, *) 

 are seen situated behind 

 the origins of the legs, 

 upon the sides of the 2d, 

 4th, 6th, 9th, llth, 13th, 

 and 15th segments, occur- 

 ring upon the alternate 

 segments, except in the 

 case of the 8tli, where 

 there is one missed. The 

 tracheae derived from these 

 spiracles pass inwards to 

 be disbributed upon all 

 the viscera, ramifying in 

 every part of the body, 

 and thus conveying air 

 throughout the system. In 

 structure these air-vessels exactly resemble those 

 of true Insects, and are equally characterized by 

 the existence of a spiral fibre in their interior, 

 whereby they are always kept permeable. 



Circulatory system. In the nature of their 

 circulatory apparatus the Myriapoda are closely 

 related to the Insects properly so called. A 

 long dorsal vessel passes from the tail towards 

 the head along the mesial line of the body. 

 The sides of this vessel, on clearing away the 



