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Biology of Pediculus humanus 
Introduction 1 . 
In the following account of the biology of Pediculus humanus, 
I have sought to bring together all that could be gathered from the 
publications of the many authors who have occupied themselves more 
or less with these insects, adding here and there my own observations 2 . 
I have sought throughout to give credit where it is due and have not 
withheld criticism where it appeared necessary. 
Lice are insects which undergo an incomplete process of meta¬ 
morphosis, i.e. they issue from the egg in an active form very similar, 
in essential particulars, to that of the adult. They are purely parasitic 
and live only on blood, P. humanus being a parasite of man and man 
only, its nearest related form occurring on monkeys. There are five 
stages in the life of the louse: (1) the nit or egg-stage, (2-4) the 1st, 
2nd and 3rd larval stages, (5) the adult stage. In passing from the 1st 
larval stage to that of the adult, it undergoes three successive moults, 
increasing in size at each successive stage. The six legs, in all stages, 
are provided with a single large, curved, sharply pointed terminal claw 
specially adapted to progression on hair; it possesses simple eyes and 
5-articled antennae; the mouthparts are adapted solely to the purpose 
of blood sucking. 
Geographical Distribution. Human pediculi appear to occur in all 
parts of the world and on all races, but precise information is lacking, 
perhaps because lice are so universal. They are recorded from most 
parts of Europe, and by Murray (1861, p. 567) and a few other authors, 
from India, China, Africa, America and Australia. 
I possess, oi' have examined up to the present, specimens from the 
following extra-European countries, the specimens answering the 
standard description of head-lice and body-lice, but some showing 
variations rendering exact determination impossible. In the latter 
case they are attributed to capitis if found on the head, and to corporis 
if found on the body: 
Capitis : Africa: from Arabs, Algeria; from Dinkas, Anglo-Egyptian 
Sudan; from negroes, S. Ashanti and Uganda. Asia : from Chinese, 
1 The investigations herein described were carried out at the request of the Local 
Government Board, the expenses entailed being partly met by grants from the Board. 
2 With the exception of the matter contained in my previous paper: “On the copu- 
latory apparatus and process of copulation in Pediculus humanus ,” Parasitology, ix. 293— 
324. The anatomy and histology will be treated in a future paper which will include 
some details regarding the mechanism of feeding and process of digestion, etc., matters 
which cannot be dealt with conveniently here. 
