P. A. Buxton 
1.41 
female; owing to their lower degree of chitinization it is not easy to distinguish 
the joints, and the skeletal rings and bands of thicker chitin; all these struc¬ 
tures are, however, present as in the adult. The length of the long seta (H 1) 
of the third leg is about 80-82 per cent, of the body length. 
THE NYMPH. 
I am unable to find that the few nymphs I have seen fall into two groups, 
and can find no support for the statement that there are small nymphs which 
produce males and large ones which produce females. It is possibly the case 
but I have no evidence that it is so. 
The nymph is about 175 microns long, by 135 broad, which gives a ratio 
of length to breadth, of 100 to 77. 
The dorsal surface (Fig. 20) differs from that of the immature female in the 
following respects. The epistome and the seta D 1 are normal, but the small 
sculptured area from which D 1 springs in the adult and immature female is 
very indistinct in the nymph. The cones scales and spines are all smaller than 
in the adult and immature female. The scales, though smaller, are well formed 
and pointed, unlike those of the larva, and are just as numerous as in the 
immature female, but they do not extend across the dorsum posterior to the 
bare area, the posterior edge of which is therefore indefinite. The plastron is 
like that of the immature female, and differs from that of the adult female. 
The species are arranged as in the adult, the formula being 3/4. A 1 and 2 
are present just as they are in the adult female. (Munro states that there is 
only one anal seta in the nymph of Sarcoptes scabiei var horn,inis.) Only one 
lateral seta ( L ) is present. From its position it is probably L 1, but I am not 
certain of this. 
The ventral surface resembles that of the immature female and larva in 
the forking of the posterior end of the sternum and second epimere, a point 
which is shown in Fig. 21 B of the ventral surface of the larva, and in the 
absence of the tocostome and its associated structures; it differs from that of 
the immature female in the absence of setae V 3 and 4. 
The capitulum is identical with that of the immature and adult female in 
all respects. The legs differ from those of the immature female in the absence 
of the long seta P 1, and in the fact that P 7 and 8, the short stiff setae on 
the fifth joint, are represented by a single seta. In respect of the spur, the 
claws, and the details of the joints the legs are identical with those of the adult. 
The posterior legs are also quite normal. The terminal seta (// 1) of the third 
leg is equal in length to about 82 per cent, of the total length. 
THE LARVA. 
The length of the larva is 140-160 microns, the breadth about 100 microns 
and the ratio of length to breadth as 100 to 66. 
The characters of the dorsal surface (Fig. 21 A) are as follows. The seta D 1 
which springs from the base of the epistome is identical with that of the adult, 
