G. H. F. Nuttall 
149 
the two forms cannot be distinguished by their gonopods. As to the gonopods 
pointing “backward' 1 or “inward,” this is frequently due to pressure or 
shrinkage, such abnormal orientation being often seen in balsam mounts. 
In both sexes, the pleurae vary greatly in appearance according to the 
degree of chitinization and pigmentation. There is no constant difference 
between capitis and corporis in this respect, but in “P. schqffi the 6th ab¬ 
dominal segment certainly projects in an exceptional manner, forming a 
ridge dorsally and ventrally which is especially evident in ungorged specimens. 
The 6th abdominal segment does not protrude exceptionally in the adult lice 
I have examined from monkeys, but it protrudes distinctly in 2nd and 
3rd-stage larvae. In corresponding larval stages of human capitis it is excep¬ 
tional to find the 6th abdominal segment protruding somewhat more than 
the others laterally. 
Claws. These are described by Fahrenholz as longer or shorter in lice 
from different races of man, as toothed in “ P. capitis angustus ” and “ P. cor¬ 
poris marginatus ,” but not toothed in European lice. These statements are 
untrue, for the claws vary in length normally and I have often seen toothed 
claws in European head and body-lice. See also the quotation from Piaget 
(p. 143). 
(c) Pigmentation in Pediculus. 
The worst blunders committed by Fahrenholz are due to his relying upon 
pigmentation in his diagnoses, this leading to his referring to various structures 
as “absent” in some pediculi and “present” in others. Thus 
The Head in “P. lobatus ” has dark brown “plates” at the sides. 
Thorax. Here the sternal plate is said to be present in “P. corporis 
nigritarum ” and “P. capitis angustus ” and “absent” in “P. lobatus ” and 
“P. friedenihaliT In “P. capitis maculatus ” there occur “holes” in the ster¬ 
num where hairs arise anteriorly, there being four holes in the 3 and two in 
the $ sternum. 
Abdomen. The degree of pigmentation of the pleurae serves to distinguish 
“P. capitis maculatus ” and “P. capitis angustus .” 
In the <$, the dorsal bands are present in “P. corporis marginatus ” and 
“absent” in European body-lice. The genital plate is present in “P. capitis 
angustus ,” “P. capitis maculatus ” and “P. humanus chinensis ,” but “absent” 
in European lice. The ventral band is a feature in “P. capitis maculatus .” 
In the $, on the last abdominal segment, there occur two brown spots 
dorsally in “P. capitis maculatus ,” indistinct plates (dorsally?) in “P. capitis 
angustus ,” and two brown plates in “ P. corporis nigritarum ” (based on one $!) 
and negro head-lice. 
It is surprising that Fahrenholz should have been so grossly misled. He 
might at least have taken a warning from Neumann’s paper (see quotation 
on p. 143). Today we know that by raising unpigmented strains of European 
P. humanus, on a black background, the “absent 1 structures of Fahrenholz 
