Gr. H. F. Nuttall 
147 
The accompanying Chart II, moreover, records measurements made by me 
on 100 $$ P. humanus race corporis (Lot 252, from tramp, Cambridge, 1918). 
The measurements relate to the antennae, head, thorax and abdomen as 
indicated on the chart, all being arranged along a straight line representing 
the anterior margin of the thorax. The lice were graded in accordance with the 
size of the thorax, the largest on the left leading to the smallest to the right. 
The length of the thorax varied between 1-1 and 0*7 mm. which may be taken 
as a good index of the relative variation in size in the lot. The great inequality 
in the length of the abdomen is due to its being more or less filled with blood 
Antennae 
—rw-vj-L 
Head 
Thorax 
Abdomen 
2 - 
-2 
Chart I. Length-measurements of Pediculus humanus race corporis, 100 arranged in 
accordance with the length of the thorax. 
and ova. The variation in the length of the head and antennae is relatively 
slight though distinct. 
( b ) Morphology of Pediculus. 
The morphological characters and their bearing on Fahrenholz’s diagnoses 
will be considered in sequence, beginning with the head and ending with the 
legs: 
Head. There is no doubt that in capitis the head is shorter than in corporis 
when typical forms are considered. The shortness in capitis is due to the more 
blunted shape of the clypeus which terminates the head anteriorly, and the 
less elongate form of the neck-like posterior portion. Nevertheless, in pre- 
