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Biology o f Pediculus human us 
When an egg is laid at the point of intersection of two or more hairs 
or fibres, these may be cemented together. The cement issues as a 
fluid having great wetting properties, for it forms a tube completely 
surrounding the greasy hair or adhering to the fibres of cloth, besides 
investing the posterior half of the egg, upon which it hardens rapidly 
as a transparent structureless membrane 1 . The latter is best seen in 
hatched eggs; it shows at most some irregular longitudinal ridges 
where it has dried in a layer of unequal thickness, the ridges con¬ 
verging toward the base of the tube surrounding the hair. I have but 
once seen a nit laid without sufficient cement, the appearance recalling 
in a moderate degree that seen in the pedunculated eggs of Chrysopa : 
a small amount of cement surrounded the hair, and from it a very 
delicate cement filament, about two-thirds the length of the egg, ran 
to the egg-base forming its only connection with the hair. 
The rapid hardening of the cement may be fatal to a female that 
fails to extrude her egg promptly after the cement flows; I have seen 
a female so firmly held to a hair by a filament of hardened cement 
that she could not tear herself loose and died attached to the hair. 
The hardened cement is exceedingly resistant to chemical agents, 
behaving like chitin in this respect; no solvent will remove it without 
first destroying the hair or fibre to which the egg is attached. When 
treated with mineral acids, acetic acid, or caustic potash, the cement 
tubes and eggshells remain after the hair or fabric has been dissolved, 
except perhaps for the detritus which may remain enclosed mechanically 
within the cement tubes 2 . 
When lice oviposit under experimental conditions upon cloth or 
felt resting on glass, they show a marked preference for-laying their 
eggs on the under surface of the fabric, even when they are constantly 
kept in the dark. In their efforts to crawl beneath cloth resting on 
glass, the insects may move the fabric about considerably provided 
its weight is not excessive. 
If narrow strips of felt are placed on end in flat-bottomed tubes 
with lice, the latter will lay most of their eggs underneath the small 
1 Some authors figure the cement covering the posterior half of the egg so that it 
recalls an egg-cup, an anterior margin or rim of cement being sharply defined as a fine 
running round the egg; I have not seen this appearance and an attempt to stain the 
cement failed. 
2 Lelean (1917, p. 141), apparently on the authority of Austen, makes the erroneous 
statement that the cement is soluble in 10 % acetic acid. Nits on hair or cloth may 
soak for days in the fluid but the cement does not dissolve. 
