14(3 
Biology of Pediculus humanus 
Delayed Hatching. 
Under certain circumstances, the hatching of the eggs of corporis 
may be considerably delayed, and it is of practical importance to know 
this. The following observations serve as examples of delayed 
hatching: 
Conditions affecting the eggs 
Eggs hatched after 
Authority 
After 8 days in tube near body, 8 
of 24 having hatched, the re¬ 
maining 16 were kept in waist¬ 
coat pocket, worn by day, hung 
up at ca. 0° C. by night 
Alternately at 30° C. and 8-10° C. 
for periods of 24 hours 
Alternately at 30° and at ca. 10° 
C. for periods of 12 hours 
At 24-5° C., damp 
Alternately at 37° C. and at ca. 8° 
C. for periods of 12 hours 
Alternately at 37° and ca. 14° C. 
for periods of 12 hours 
After 2-3 weeks at 9° C., trans¬ 
ferred to “favourable tempera¬ 
ture” 
After 24 hours at - 10°, trans¬ 
ferred to 26-30° C. 
over 4 weeks ... 
33 and 35 days 
(Only 4 hatched out of many; 
3 hatched 33rd day, 1 on 
35th day. None before or 
after) 
26 and 27 days 
(Only 4 hatched out of many. 
None before or after) 
a few hatched up to 23 days 
only 2 out of many, in 16 days 
only 4 out of many, in 15 days 
15 days 
17 days (6 eggs) . 
Warburton, 1911 
Nuttall 
Bacot, n. 1917, p. 248 
Nuttall 
>5 
Heymann, 18. vm. 
1915, p. 305 
Widmann, vnx. 1915, 
p. 293 
The following authors’ records of delayed hatching do not state the conditions: 6 weeks 
(Fantham, 1912, j>. 514); 18 days (Nocht and Halberkann, 1915, p. 626); 21 days (Zupnik, 
1915, p. 564); 18-22-30 days (Swellengrebel, 1916, p. 4). 
In Bacot’s and my experiments the time is reckoned from the day the nits were laid. 
Summary relating to the time required for Hatching. 
Corporis eggs do not hatch at 22° C. or below; a favourable tempera¬ 
ture is attained at about 25° C., but development is slow, lasting 16 
days; at 30° C., hatching occurs in 7-14 days, mostly in 11-13 days; 
at ca. 35° C., the eggs being kept near the human body, hatching occurs 
in 6-8 days; at 36-37° C., hatching occurs in 4-8 days, mostly in 5-6 
days; at 38° C., hatching is slightly retarded, and the eggs die without 
hatching when kept at 40-45° C. Eggs do not hatch before the 4th 
day under any circumstances. Most of the eggs laid on the same day 
hatch within 48 hours of each other, but they may hatch during 4-8 
days, there is therefore no great uniformity in the hatching period. 
