138 
Biology of Pediculus humanus 
eggs somewhat more closely aggregated. I therefore conclude that there 
is no difference in the matter of alignment of eggs deposited by the lice. 
(2) Regarding the laying of eggs on tivo or more hairs and at the 
intersection of hairs: Bacot (loc. cit., Fig. 4) states that corporis lays 
more eggs at the intersection of hairs than does capitis under experi¬ 
mental conditions. A count of eggs laid on hair-frames and skeins 
of hair in my experiments showed no such difference. Thus out of 
110 eggs laid by corporis there were 6 laid where hairs crossed; out of 
117 eggs laid by capitis there were 7 laid where hairs crossed. On looking 
over nit-bearing hairs preserved from old experiments as examples 
of the oviposition of corporis on hairs, placed haphazard in a tube, 
a count revealed that of a total of 79 eggs, 57 were laid on single hairs, 
14 upon two fine hairs which lay closely in contact and 4 at the intersec¬ 
tion of two hairs. The haphazard arrangement of hairs in boxes would 
therefore appear to have misled Bacot. To test the matter the arrange¬ 
ment of the hairs should be strictly comparable. When hairs are 
placed loosely in a vessel, they will continually shift about owing to 
the movements of the insects, and uncontrollably irregular results must 
follow. When two fine hairs happen to lie closely apposed they are 
grasped by the gonopods as if they were one hair, this (Bacot, loc. cit. 
Fig. 3), like the occasional deposition of eggs on the glass surface of the 
cell, may happen with capitis as well as corporis. 
The “Homing Instinct” in respect to Oviposition. 
Whereas I have frequently observed that corporis lays eggs about 
one spot on a piece of cloth, the subject received no particular attention 
until the appearance of Bacot’s paper (n. 1917, p. 232) wherein he 
^refers to this tendency. Finding it difficult to enumerate the eggs 
laid by a female when they were ranged close together, Bacot sought 
to persuade the female to lay elsewhere by shifting the piece of cloth 
about within the breeding box in which she was confined. He states 
that as a rule he was unsuccessful, “there seemed to be some attraction 
which led to the deposit of fresh eggs where others were already laid.” 
Although he does not specifically state that he observed the tendency 
in isolated females, it may be assumed that he did so. The tendency 
is said to be less marked in capitis. 
As the presence of such an instinct in lice is of interest, I resolved 
to repeat Bacot’s experiment under somewhat altered conditions in so 
far as a larger piece of cloth was chosen, and an isolated female (without 
a male) was allowed to wander about upon it. 
