148 
Biology of Pediculus humanus 
air are seen passing back from a large bubble in front of tbe moutb 
into the pharynx (Fig. 9, 8) and onward into the gut. This air passes 
in by diffusion through the operculum. The air accumulates in the 
gut and is forced backward and out through the anus and accumulates 
to form an air-cushion behind the larva, pushing it more and more 
against the operculum. The play of the pumping muscles of the 
pharynx can be seen in the head. The eyes are now jet black and 
circular. The head is pressed against the operculum, and with the 
anterior part of the thorax, is strongly flexed ventrally, the palps 
lying between the basal segments of the forelegs. Fig. 9, 14, shows a 
larva at this stage drawn immediately after its removal from the shell; 
a bubble is seen in its pharynx, and another large bubble in its midgut 
to the right of the circular disc-like organ which lies in a depression of 
the ventral surface of the midgut. 
The manner in which the Larva issues from the Egg. 
When the larva is ready to emerge, it begins to pump in air very 
rapidly, the bubbles being distinctly seen through the transparent 
glassy shell as they pass backward into the gut. When the pumping 
begins the larva fills the upper three-quarters of the shell, and as the 
air accumulates inside the gut, the end of the abdomen extends down¬ 
ward and finally impinges upon the base of the shell. If the micropyle 
apparatus is occluded by means of glycerine or oil, the pumping ceases 
and the insect dies. As the air expelled from the anus accumulates 
behind, the larva is pushed against the operculum; this pressure of the 
air-cushion finally overcomes the resistance of the operculum and the 
latter springs open. The fore part of the larva, which has acted like 
a stopper to the air, is slightly extruded after the operculum has opened. 
The head of the larva now assumes the normal position, and the first 
pair of legs emerge. Meanwhile the pumping process continues actively, 
increasing the pressure from behind. The larva now protrudes its 
second pair of legs, and the third pair soon follows, hatching being 
completed (Fig. 10). 
The first to study this highly interesting process was Sikora (vm. 
1915, p. 530), whose observations I gladly confirm and extend. Hase 
(1915, p. 25) attributed the springing open of the operculum to the 
pressure of the head of the larva, and, although he observed the pumping 
process, he failed to catch its significance. Muller (1915, PI. Ill, Fig. II), 
who cites Hase, illustrates the emerging larva. 
