92 CERTAIN PARASITIC INSECTS. 
of maxille and maz’, the second pair of maxille, or labium. 
At this time the embryo may be compared with that of the 
dragon fly of the same period of growth (Fig. 24 c, clypeus; 
l, antenne; 2, mandibles; 3, maxille; 4, labium; 5, 6, 7, 
legs.) We see that the mouth parts of the louse, so unlike 
those of other adult insects, are originally similar to them. 
Figure 21 represents the mouth parts of the same insect a 
Fig. 20. Fig. 21. 
Fig. 22. 
Fig. 23. 
DEVELOPMENT OF THE MOUTH PARTS OF THE LOUSE. 
little farther advanced, with the jaws and labium elongated 
and closely folded together. Figure 22 represents the same 
still farther advanced; the mandibles (mad) are sharp, and 
resemble the jaws of the Mallophaga; and the maxille 
(max!) and labium (maz?) are still large, while afterwards 
the labium becomes nearly obsolete. Figure 23 represents 
the mouth parts of a bird louse, Goniodes ; lb, is the upper 
