P. A. Buxton 
129 
Robin’s drawings of the mouthparts, etc., of Sarcoj)tes are better than those 
of any of his predecessors or successors, but he made serious mistakes in inter¬ 
pretation. It appears that he was too much inclined to read a knowledge of 
insect anatomy into his observations on Sarcoptes. The result is that he re¬ 
garded the pedipalps (or “ palps ” in the acarological but not entomological 
sense) as the homologues of the maxillary palp of insects; these pedipalps, or 
“palps” are segmental appendages in the strict sense of the word and therefore 
comparable to the whole of an insect appendage. Having made this mistake, 
a most natural mistake too in 1860, he searched for the rest of the “maxilla,” 
and attached this name to the stout chitinous knob ( kn) and the two chitinous 
bands (b 4, b 5) which unite to form it. In his definition of the Sarcoptidae he 
says (1860, p. 196): “a rostre pourvu de machoires inermes tres petits portant 
des palpes maxillaires lateraux, voluminaux, a trois articles”; he adds that 
the “machoires ou maxilles” are “soudees ensemble par la ligne mediane.” 
Robin’s mistake was copied by Railliet, whose figure was copied by 
Neumann, whose description repeats the error. The mistake does not merely 
affect our idea of the structure of Sarcoptes for this supposed union of the 
second appendage to form a median unpaired organ has become one of the 
accepted characters of the Sarcoptidae, and is figured as such by Berlese 
(1912, p. 11) in a figure which shows diagrammatically the supposed differ¬ 
ences in the structure of the capitulum in different families of Acarina. I sub¬ 
mit that this is an important, if academic, point, and that none of these 
authors produce evidence that the median unpaired structure is part of the 
pedipalp, or of any other appendage. It appears better to regard it as formed 
from the basis capituli, and to admit that we know nothing of its derivation 
in the embryo. It is not generally considered that any median ventral part 
of the head of spiders or scorpions, or other Arachnoidea represents a part of 
a pair of fused appendages, and it is not necessary to believe that this is the 
case in the Acarina. 
I find myself in disagreement with Robin on a second point, which is of 
minor importance. The cheek-pieces are so thin and colourless that their mere 
detection is a matter of difficulty. Robin figures them fairly accurately but 
insists that they are the lateral lips of the camerostome, in fact prolongations 
of the body integument comparable to the epistome; I have convinced myself 
that they do not spring from the body at all, but are a part of the basis 
capituli itself, a ventral laminar prolongation of it arising from the transverse 
bar (b 4), and passing forwards beneath the palps. Fiirstenberg (1861) figured 
and described the cheek-piece, which he called “backe,” and his figure is at 
any rate accurate in this point that he derives the cheek-piece from the basis 
capituli. He made, as is well known, the extraordinary mistake of providing all 
his Sarcopts with two pairs of chelicerae; whether as Warburton suggests he once 
observed a Sarcoptes in process of moult and so became possessed by a fixed 
idea that there were four chelicerae, or whether he saw not only the extremity 
of the chelicerae but also of the erect bodies of the lower lip we do not know. 
Parasitology xm 
9 
