274 SarCoptic Scabies 
portance. They are chitinous bars produced into the body from the skeletal 
tissues of the legs, and are arranged as follows: 
From the first pair of legs the epimeres run inwards and meet just behind 
the base of the rostrum and are then produced backwards in a single sternal 
rod, ending in a fairly sharp point; the epimeres of the second legs are free 
and slightly curved, converging towards the sternal bar without reaching it, 
and ending at about the same level. Precisely how they terminate seems 
doubtful, whether in rounded knobs or in a slight fork. The epimeres of the 
third and fourth legs are short and curve towards one another till they nearly 
meet, but they do not fuse. 
Immediately behind the end of the sternal bar is a transverse slit—the 
tocostome, or aperture for egg-laying, guarded by three very short bristles 
(see PI. XV, fig. 11). There is also a pair of short bristles one on either side of 
the middle of the sternal bar, and another short pair between the fourth pair 
of legs. 
The legs. The two anterior pairs of legs arise from the margin of the body 
and are larger than the third and fourth pairs, which arise from the under 
surface of the animal. Moreover the two 
first legs terminate in ambulacra (ventouses), 
long tubular processes ending in a bell¬ 
shaped sucker, while these ambulacra are 
not found on legs 3 and 4, each of which 
is produced into a long bristle. Each leg 
consists of five articles (coxa, trochanter, 
femur, tibia and tarsus according to Du- 
breuilh and Beille), and has a strong chitinous 
skeleton, each article being strengthened by 
a chitinous ring, and there being also, ap¬ 
parently, an obliquely placed ring of chitin 
connecting the rings of the first two articles 
(Text-figure 2). The anterior legs have three 
claws, one (discovered by Megnin as de¬ 
scribed above) on the inferior side of the 
trochanter, and two, of unequal size, at the 
extremity of the tarsus near the origin of 
the ambulacrum. The ambulacrum itself is about as long as the whole 
limb. The legs are also furnished with a few bristles and some short spines 
(piquants). 
The rostrum. The mouth-parts are enclosed in a sort of incomplete chamber, 
the camerostome formed by four prolongations of the integument—the epistome 
above, the cheeks (joues) on either side, and the hypostome (levre) below. 
They consist of six pieces, arranged in two rows; above are the chelicerae and 
pedipalpi, and below are the machoires (? labial palps) soldered to the sides 
of the hypostome and meeting posteriorly in a rounded plate, the mentum. 
Text-figure 2. Rostrum and leg of 
Sarcoptes scabiei (after Railliet). 
