210 



NATURAL HISTORY OF ARTHROPODS. 



to give a firm hold for the penetrating bristles, arranged as chitinous strips in a long, 

 slender, flexible tube, terminated by four very minute lobes, which probe to the capil- 

 lary vessels of a sweat-pore. (Fig. 290.) The blood being once reached a current is 

 maintained by the pulsations of the pumping ventricle and the peristaltic movements 

 of the stomach. The legs are scansorial, armed with a long and powerful articulated 

 curved nail at the tip of the tarsus, which is opposed by a toothed projection of the 

 inner angle of the tibia. 



Two genera at present compose this family, of which the first is Pthirius, with 

 only one species, the Crab-louse, P. pubis. The body of this creature is lyrate, 

 pale yellowish or white ; the head deeply seated between the prominent shoulders of 

 the thorax, with small, round, dark eyes on each side, five-jointed antennas, and chest- 

 nut-brown claws. There are four prominent processes on each side of the abdomen, 

 beset with long bristles, the posterior pair being the longest and most slender. It is 

 about three-fourths of a line in length, by one-half of a line in breadth. A marked 

 difference from all the other members of this family will be noticed here in the form 

 of the fore-legs. These lack the heavy claws of the other pairs, and have, instead, a 

 slender tapering form with a very slightly curved tarsal nail. The effect is to give 

 them more ready means of moving over flat surfaces, and of turning over if thrown 

 upon the back. Their legs do not rotate freely upon the coxal articula- 

 tions, and hence the claws must always be directed nearly downwards. 

 These offensive vermin affect the pubic region and armpits of man ; 

 stretching themselves out flat, holding tight to the cuticle, and inflicting 

 a most irritating puncture into the flesh of unclean and careless persons. 

 The other genus is Pediculus, which is represented by the common 

 Louse of the human head, P. capitis, and the Body-louse, P. vestimenti. 

 In these the thorax is quite distinct, narrower than the abdomen, with 

 the head more or less conical and contracted at 

 base. The eyes are usually placed on the sides, 

 just behind the widest part of the vertex, but 

 occasionally a little way inward from the margin; these are 

 also simple as in the preceding genus. All the legs are armed 

 with the claw-like nail and the opposable tibial spur, and in 

 some forms there is a fleshy cushion between these instruments. 

 The apparent number of abdominal rings ranges from seven 

 to nine, and this part of the body is especially invested with 

 a series of rigid bristles near the sutures and on the outer 

 margins. Spiracles are conspicuous iipon both the sides of 

 the thorax and abdomen ; those on the latter being sometimes 

 placed far out next the margin. 



In the first named species which is confined to the head of 

 man we see a narrowly elliptical form, a little squared on 

 the sides of the thorax ; the margins of the abdomen more 

 deeply scalloped in the female; the general color pale yel- 

 lowish, with the outer edges of the thorax and abdomen dark 

 brown or gray, and the nails pale brown. It is met with 

 chiefly upon the heads of neglected children, where it lives 

 among the hair, and to which it glues the oval eggs, attaching them mostly by the 

 pointed end. These eggs are called nits, and under favorable conditions hatch in 



FIG. 288. Pcil- 

 iculus capitis, 

 head-louse. 



am 



FIG. 289. Embryo louse; a, 

 antenna; am,amnion; h, 

 head. 



