A. Bacot 
233 
various methods of shifting the piece of cloth, turning it, so that the 
exposed surface went against the side of the box, the addition of a second 
piece of cloth, etc., were tried in an endeavour to get the eggs spread, 
instead of clustered. As a rule these attempts were unsuccessful, there 
seemed to be some attraction which led to the deposit of fresh eggs 
where others were already laid. 
P. capitis ?2 occasionally exhibited the same tendency, but it was 
never so marked or “wilful” as with those of P. hunianus. Another 
habit that was marked in the body louse and less noticeable but still 
to be observed with P. capitis, was a tendency to gregariousness shown 
by clustering, especially on the part of the larvae and nymphs when 
about to moult. 
Pairing may be seen at any period of the day or night on the part of 
both species, the insects remaining together for a considerable time; 
periods of over an hour were observed, but I failed to ascertain what 
the limits were. 
Both species show a very definite negative heliotropism, moving 
towards any shadow or dark coloured object in their vicinity. General 
observation suggested that their actions difiered somewhat, however, 
according to whether they were at the time of exposure to light resting 
on a dark or a light surface. The following experiment was carried 
out with P. humanus: 
Two eight inch squares of paper, one black and the other white, 
each having a sufficiently roughened surface to afford good foothold, 
were placed near together about two feet from a window. The lice., 
at each trial being emptied out of a tube on to the centre of the paper. 
Two batches of lice were used, each comprised five females and 
four males; eight trials were made on each paper—the batches being 
transposed from black to white and vice versa after each trial. 
While these experiments strengthen the idea suggested by my 
general observations, viz. that there is a difference between the 
behaviour of the insects dependent upon their being on a light or dark 
surface when exposed to the light, their movements being less assured 
in the former case, the result is not so striking as I was led to expect. 
Had the papers been broader all the active insects would have reached 
the end farthest from the source of light, as all their tracks towards 
the sides were diagonals in this direction. 
The sluggishness recorded is, with one exception, due to the 
inactivity of three d<?; of the 15 records 14 were due to the inaction 
of these three individuals. 
