142 Sarcoptes 
but the small sculptured area is absent. The plastron is as in the other immature 
stages, that is to say it is represented by a smooth rectangular space the sur¬ 
face of which is free from shagreening. Only two cones are present, the absent 
one being the anterolateral. The scales are few in number, small and blunt. 
The bare area is like that of the nymph, crossed by ridges, and only enclosed 
by scales in front and at the sides. Only five pairs of spines are present, and 
the formula is 2/3. As in the nymph one lateral seta only (L) is present. 
The ventral surface (Fig. 21 B) shows the following features: the presence 
of V 1 and V 2 and absence of V 3 and V 4, as in the nymph; the forked end 
of the sternum and second epimere as in the nymph and immature female; the 
presence of a single anal seta (A) on each side and the absence of the fourth leg. 
Fig. 21. Sarcoptes scabiei var equi. A, dorsal, and B, ventral views of larva. A, anal seta; an, 
anus; cap, eapitulum; co, cone; D 1, first dorsal seta; e 1-11, epimeres; H 1, terminal seta of 
third leg: L, lateral seta; V 1, first ventral seta; 111, third leg. 
The eapitulum is in all respects like that of the other stages. The legs are 
like those of the nymph, in the absence of P 1, and the presence of a single 
seta in place of P 7 and 8. In other respects they are normal. The fourth leg 
is absent. The ratio of the length of the seta H , of the third leg to the total 
body length is 89 per cent, to 97 per cent. 
The gradual appearance of the adult characters through the larval, 
nymphal and immature female stages is perhaps worthy of being summarized. 
The eapitulum and its setae appear to be identical in all stages, though I must 
confess that I have made no dissections of the eapitulum of the early stages. 
The principal setae, D 1 and 2, V 1 and 2, A 1, and the general shape of the 
