P. A. Buxton 
143 
leg, and of its several joints is the same in the larva as it is in the adult female. 
In the following respects the larva differs from the nymph; it lacks the fourth 
pair of legs, and the second anal bristle; its dorsal armature consists of only 
two cones and five spines, on each side, and of a relatively small number of 
scales. The nymph and larva lack the setae V 3 and 4, and P 1 and either P 7 
or P 8, and one of the lateral setae (L 2?), but in other points resemble the 
immature female. The larva, nymph and immature female resemble each 
other but differ from the adult principally in the absence of the tocostome, 
and its setae and of the genital operculum; but also in the forking of the 
sternum and second epimere, the ridging of the bare area, the imperfect 
cap 
Fig. 22. Sarcoptes scabiei var. equi. Egg, in which is seen the ventral surface of a larva which is 
ready to emerge. Only some of the most conspicuous setae are shown, an, anus; cap, capi- 
tulum; H 1, terminal seta of posterior leg; L, lateral seta; P 9, ninth seta of second leg; I, 
II, III, legs. 
separation of notothorax and notogaster, and the absence of shagreening on 
the plastron. It is therefore true to say that the assumption of the adult 
characters occurs gradually at each moult, and that no one moult more than 
another produces very marked changes. 
THE EGG. 
The length of the egg, measured without compression is 167—175/x, the 
breadth 88-97/x, and the ratio of length to breadth 100 to 51*5-56*8. The 
surface of the egg is smooth, without sculpturing. The example figured (Fig. 22) 
is about to hatch and the enclosed larva is seen by transparency. 
