118 
Sarcoptes 
the furrow between the notothorax and notogaster may be obliterated. It 
was from a specimen in this condition that Fig. 2 was drawn. The terms 
cephalothorax and abdomen which have been used for these two portions of 
the body are unsuitable because as Warburton says (l.c. p. 272) they bear a 
different meaning when applied to other groups of Arachnoidea; I might add 
that application of these terms to any Arachnoidea is open to objection. 
The Dorsal Surface. 
The dorsal surface (Fig. 1) is covered with fine parallel ridges which gener¬ 
ally run transversely except where they follow the lateral contours of the body, 
or bend partially round the anus. A fold of the dorsal integument, the epi- 
stome (Plate VII, ep), covers the insertion of the basis capituli into the camero- 
stome. The camerostome is a hollow in the front of the body for the reception 
of the capitulum. It cannot be seen from above. The epistome, which is in 
fact the dorsal wall of the camerostome, is not transversely ridged. Across its 
posterior part stretches a small area covered with shagreened sculpturing and 
containing two relatively large pits from which the setae (D 1) arise. This 
small shagreened area was noticed by Railliet in 1887 in Sarcoptes laevis, 
which is now placed in the genus Cnemidocoptes Fiirstb., but it has not I 
think been described in any Sarcoptes in the restricted sense. Lobes of integu¬ 
ment similar to the epistome cover the bases of the first and second legs; that 
covering the base of the first leg is particularly prominent, for the dorsal 
epimere surrounds a raised portion of the integument, the epaulette (el). 
There is no dorsal epimere and no epaulette in relation to the second leg. The 
ridges into which the greater part of the integument is thrown are faint and 
often interrupted in the mid-dorsal region over the greater part of the noto¬ 
gaster (see p. 119); they are absent from a small area on either side of the 
anus, and from a conspicuous roughly rectangular area on the notothorax. 
This area is the plastron of most authors including Railliet; the rugose area 
of Munro. (The “plastron” of Robin is on the ventral surface; it is the place 
of union of the first pair of epimeres with the sternum.) 
The shape of this plastron (pi), as I shall call it, is shown on Plate VII. Its 
width is about 21 times its extent from before backward; the anterior margin 
is convex, the posterior straight; the anterior angles are acute, the posterior 
obtusely rounded. It is extremely difficult to represent this structure in a 
drawing, but I have endeavoured to do so in Plate VII. In Fig. 1 I have stippled 
it, so as to show its extent, but have not been able to indicate that the whole 
surface is shagreened; under an oil-immersion lens the appearance is as of a 
great number of points of light, regularly arranged upon a yellowish back¬ 
ground. It is very slightly more strongly chitinized, and slightly browner in 
colour than the rest of the integument, but it is the easiest thing possible to 
overemphasize its degree of chitinization in drawing it. In fact the very word 
plastron is unsuitable, because it makes one think of an impenetrable plate 
of mail, but it is at any rate to be preferred to “rugose area,” a term which is 
