152 
Biology of Pediculus liumanus 
The empty shells after a time break away anteriorly, but the basal 
portion surrounded by the thicker mass of cement, and the cement 
tube on the hair, remain unless mechanically removed. Rows of empty 
nits or tubes and fragments of eggs are frequently seen on hairs at whose 
bases there are unhatched eggs in different stages of development; this 
being due to the growth of the hair awav from the scalp close to which 
the eggs were originally laid. 
Fertility. 
The proportion op Eggs that hatch and that are Fertile. 
-(a) Corporis. 
According to Sikora (vm. 1915), the first and last eggs laid by a 
female are equally fertile. This statement, however, requires qualifi¬ 
cation, for the fertility of the eggs depends upon copulation having 
taken place and the female having received a sufficient supply of sper¬ 
matozoa to fertilize all the eggs she lays. There is no evidence that all 
the eggs laid by a female are fertile, in fact, as I have repeatedly seen, 
occasional infertile eggs are laid by fertilized females. 
Bacot (n. 1917, pp. 241-244) states that usually but 33-65 % and 
at times 75-81 % of the eggs are fertile. In four sets of about four 
pairs (d $) observed for a period of some eight days, during the 12th-30th 
day of the females’ lives, 91-97 % of the eggs were fertile. The 
greatest number of fertile eggs laid by a single female was 115. The 
following records relate to the percentage of fertile eggs, as tested by 
hatching, which were laid by many females of different ages. The first 
three records are extracted from Hindle’s ms. notes, the last three are 
'from my own more recent observations. The females were kept with 
males, were fed twice daily, and, like the eggs, were maintained in the 
thermostat. 
Proportion of eggs that hatched. 
Temperature 
at which 
No. of 
eggs were 
kept, ° C. 
eggs that 
were laid 
30° 
203 
30° 
322 
30° 
267 
30° 
150 
30° 
216 
37° 
161 
No. of 
eggs that 
hatched 
0/ 
/o 
160 
78-8 
238 
73-9 
154 
57-7 
105 
70-0 
149 
69-0 
87 
54-3 
