A. D. Peacock 
99 
specimens so treated may be examined under the low power to see if the parts 
are extruded. This method was successful on the first trial, the stabbers 
being extruded fully, but scores of attempts since have resulted in failure. 
Occasionally a specimen may be obtained which shows the stabbers partly 
out. Better results are possible with very young lice. The use of ethylchloride 
as a killer gave no better success than chloroform. 
Only occasionally was a binocular dissecting microscope available and 
many dissections were made under the objective of an ordinary microscope. 
With a little practice the stabber sac and its organs may be readily freed from 
the head. To do this three cuts may be made with the edge of a triangularly 
sharpened dissecting needle, two cuts being sagittal along the lateral chitin 
of the head and one transversely along the post-dorsal chitin. The dorsal 
chitin of the head, after scraping beneath it, may be removed like a lid. With 
a little more dissection the whole sac and its contents may be isolated. 
Specimens for section cutting were obtained by fixing in 5 % formalin 
for one day; dehydrating in alcohol, 50%, 75%, 90%, absolute, twelve 
hours in each; clearing in xylol, one day at least; placing in a mixture of 
xylol and paraffin wax (m.p. 54° 0.), equal parts, for twelve hours and then 
in wax for periods ranging from 30 minutes to one day. Sections were cut 
about 10/x in thickness, using an exceedingly sharp razor and a Cambridge 
rocking microtome. 
The choice of stains only permitted one series of sections being treated 
with Mayer’s haematoxylin, intensifying the blue with ammonia and differ¬ 
entiating with eosin. This method gave the best results and all mention in 
the text to the colours of stained tissue refers to it 1 . 
In interpreting sections, two important items should be borne in mind: 
(1) the shrinkage and distortion of tissue and organs due to treatment, (2) the 
degree of protrusion or retraction of the mouth-parts. 
GENERAL FEATURES OF THE HEAD. 
Three regions may be distinguished in the head of the louse when viewed 
dorsally (Text-fig. Ill) (1) the anterior bluntly pointed clypeus, (2) the central 
broader, somewhat domed epicranium , (3) the posterior, narrower occiput. 
Anteriorly from the clypeus there often projects a small, short, blunt rostrum 
—the “ haustellum” The lateral chitin of the clypeus is thickened and fre¬ 
quently pigmented dark brown. The epicranium, just behind and laterally 
to where it merges with the clypeus, bears the antennae and, at its broadest 
region, laterally, also bears the eyes. The lateral chitin behind the eyes, as 
far back as the occiput, is thickened and often pigmented like that of the 
clypeus. The posterior part of the occiput is sunk into the thorax. 
1 The main conclusions are based on the examination of twenty cleared specimens of heads, 
a few dissections and a single series of transverse sections cut by Capt. Dunn. Certain details, 
however, have been worked out from the sections of another sixteen series (eight transverse and 
eight longitudinal) which had not been so successfully prepared. The gross structure of the parts 
was drawn with the aid of an Abbe camera lucida. 
t 
7—2 
