296 SarCoptic Scabies 
used to denote a definite area with a granular or rugose surface and some¬ 
times more distinctly chitinised than the rest of the integument. These are 
what Munro calls “rugose areas” and what he very diagrammatically depicts 
as dark patches, one on the notothorax of both o and $, and tw o on the 
notogaster of the <?. Megnin says that in equi the notothoracic rugose area 
(plastron) is of a faint yellow colour. In the human sarcopt it seems to be 
very inconspicuous, and it does not appear at all in many of the best ac¬ 
credited figures of this form. Gerlach shows it as a bare, somewhat rectangular 
light patch. It is present in all the varieties, and may perhaps be regarded 
as a sort of rudimentary scutum, such as is found in many arachnids. Its 
shape and dimensions are considered to be of taxonomic importance, and 
indeed, if it be of the nature of a scutum, it is just one of those structures in 
which forms which are really distinct might be expected to exhibit differences. 
In the Acarina for the most part the males of the various species are more 
distinctive than the females. So far, in the genus Sarcoptes, only very slight 
differences between the males of the various forms have been noted, the most 
important being the relation of the epimeres of the posterior legs to the 
epiandrium. The smaller size, and the relatively small number of the males, 
may have militated against their receiving due attention, but if they are all 
as similar as the various observers have apparently found them this would 
certainly argue a very close affinity between the different forms of Sarcoptes. 
When once the chaetotaxy and armature of a single form have been 
definitely established, Sarcoptes taken from characteristic cases of scabies in 
other animals may be compared with it as occasion arises. All possible care 
must again be taken that the case shall be one of the ordinary scabies of the 
animal, and not a temporary infection from an animal of a different group. 
Much reliance has been placed upon mere size. When the very wide range 
given in the measurements of the adult female and male of all the so-called 
species is considered, it is not easy to believe in the great importance of this 
character. It would at most indicate a distinction of race in the absence of 
more significant differences of structure. Some writers have arranged the 
varieties they recognise in order of size. Dubreuilh and Beille, for instance 
(p. 12), give as a descending series suis, equi, lupi, caprae, cameli (our drome- 
darii), ovis and hominis, the first-named attaining 500/x in length and the last 
300/x. It is admitted that, notwithstanding considerable inequality in the 
size of individuals, there may still be a noticeable difference in average size 
in the forms found on different hosts. Care should at least be taken that the 
average size attributed to any form be based on the measurement of a suffi¬ 
cient number of specimens. Where transference from one animal to another 
is possible it would be a very interesting observation to note whether it is 
accompanied by any change in average size. 
The proposed research will no doubt include experiments in the artificial 
transference of scabies from one animal to another, and the views and the 
warnings—of Delafond and Bourguignon in this connection will be especially 
