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Biology of Pediculus humanus 
and to remain clinging to each other requires to be counteracted, otherwise 
it may vitiate the experiment. The difficulty is met through separating the 
insects prior to each test and distributing them singly over the floor of the 
experimental cell. 
Methods. 
My experiments were conducted on bright sunny days in May, and mostly 
in the open air on the flat roof of a building. The apparatus employed (Fig. 1) 
was of a simple improvised character. The lice were confined beneath an 
Fig. 1. Apparatus used for experiments on the reactions of lice to light and colour. 
inverted, flat, circular glass dish, 22 cm. in diameter, with vertical sides 2 cm. 
in depth, hereinafter called the cell (Fig. 1 a). The cell rested upon a flat- 
topped stool (c) with rotating top. To prevent the light from falling otherwise 
than vertically upon the insects, the top of the stool was surrounded by a 
quadrangular funnel of dull black sateen (d), the funnel measuring ca. 60 cm. 
in height and 35 cm. across. The funnel was constructed by tying 4 rods of 
glass or bamboo (e) vertically by means of string (/) to the sides of the backs 
of two chairs (g) which were placed back to back on either side of the stool; 
