172 
Biology of Pedicnlus humanus 
chitinous teeth which are inverted when the suctorial apparatus is 
withdrawn. The hooklets serve to anchor the head of the louse to the 
skin; they are figured by .Swammerdam. Schjodte (1866, pp. 213 
et seq.) found ffhat the haustellar teeth offered a slight but appreciable 
resistance when he attempted, with the aid of forceps, to pull the head 
of the louse away gently from the skin to which it was anchored. 
Many lice, when feeding, tilt the long axis of their bodies almost 
vertically to the skin surface; this seems to me attributable to the firm 
grip afforded by the haustellar teeth which permits a relaxation of the 
efforts of clinging with the legs and of depressing the head; this position, 
moreover, places the head in the most favourable position for maintain¬ 
ing the grip with the haustellar teeth and using the piercing mouthparts. 
In other words, the haustellum with its teeth acts in a somewhat similar 
manner to the mouthparts of a tick in anchoring the parasite to the host, 
so that little or no effort is required by the legs. Having anchored 
itself by the haustellum, the louse protrudes the piercing organs and 
proceeds to pump. It may draw blood at once or repeated efforts may 
have to be made at different places before blood is successfully drawn. 
Assuming that blood is found, the insect proceeds to pump it in by 
means of its pharyngeal apparatus which can be readily seen with a 
hand lens or better under a binocular microscope. The pulsations of 
the pump are so rapid that they can scarcely be counted. Sikora (vm. 
• 1915, p. 531) states that there may be 150 pulsations a minute, but this 
seems to me largely guesswork. From the pump, the blood is propelled 
back through the fine tubular oesophagus into the midgut whose 
peristaltic movements become extremely active. As the intestine fills, 
excreta are commonly voided in more or less profusion. The time 
occupied in feeding, the amount of blood imbibed and of excreta voided, 
are largely dependent upon the state of hunger. 
The frequency with which Lice feed. 
The louse larva feeds at once on emerging from the egg as was first 
noted by Warburton (1911) and has since been confirmed by Fantham 
(1912) and Swellengrebel (1916); the latter’s statement that larvae 
feed more promptly than adults is contrary to my observations on 
equally hungry larvae and adults. After helping a larva to emerge, 
by means of a needle, I have transferred it on the needle-point to the 
back of my hand and seen it suck blood immediately. Later stage 
larvae and adults are ready to feed very soon after moulting; thus 
Sikora saw an adult feed 45 minutes after ecdysis. 
