0. Warburton 
277 
burrow daily excavated was between two and three millimeters. Torok and 
Dubreuilh have shown that the galleries are entirely confined to the corneous 
' layer. 
A fairly constant characteristic of Sarcoptes burrows is the presence of 
vesicles (vesicues perles), minute translucent indurated swellings, which are 
regarded as second only to the galleries themselves in diagnosing scabies. It 
was these vesicles which misled investigators at the beginning of the 19th 
century, for they sought in vain for the mite in their interior—though Moffett 
had stated as early as 1634 that it was not to be found in them, but in their 
neighbourhood. The vesicle, indeed, forms below the gallery, a short distance 
behind the burrowing mite. The gallery and the vesicles seem to be directly 
attributable to the Sarcoptes , but the other complications which so frequently 
attend severe scabies must be regarded as secondary. 
Oviposition. The mite deposits eggs in groups of 2-4 (Gerlach says 3-6) 
as she proceeds with her burrowing, resting after each act of deposition. 
Black masses of excrement are found in the neighbourhood of the eggs. The 
eggs are oval, 150 x 100/x. They appear to be laid in a varying condition 
of development, which may partly account for the very varying incubation 
periods allowed by different writers. Bourguignon gives ten days and 
Fiirstenberg seven days, but Gerlach states that this is certainly inaccurate, 
and that the usual period is 64-76 hours. Munro agrees with the latter 
estimate when nothing has happened to delay matters, but he says that 
partially developed eggs may have their development arrested by unfavourable 
conditions and afterwards resume it. 
Unless disturbed the female makes a single burrow and dies at the end of 
it. The burrow is always sinuous, and just the width of the mite. It may 
attain 3 cm. in length. At intervals there are holes in the roof—to admit air 
or for the egress of the larvae and nymphs. The number of eggs is doubtful— 
possibly because few burrows are entirely undisturbed. The largest number 
actually found in a burrow seems to be 21, but there exists a pretty general 
belief that the female lays in all about 40 or 50 eggs. 
The larvae. Several authors (Hebra, Railliet, Dubreuilh) state that the 
larva moults three or four times. Munro found no evidence of this. They 
live in the burrows and bore into its floor, or emerge and burrow deeply into 
the skin outside—more deeply, according to Gerlach, than the females them¬ 
selves. 
The nymphs. Nothing has been observed as to the habits of the first- 
stage nymph. The second-stage nymph (femelle pubere) makes a burrow like 
that of the adult but smaller, and devoid of vesicles. These short burrows have 
lateral branches or pockets excavated by the male (Munro, p. 22). 
Megnin (1893, p. 132) says that he has found the human Sarcoptes on 
small house-dogs, and very frequently on ferrets, and that Railliet has found 
it on rabbits. 
