G. H. F. Nuttall 
*219 
concluded that “ there seems no doubt that the method of inheritance is 
alternative, but whether associated with the sex or not is not yet decided.” 
Pigmentation in Pediculus is not an hereditarily transmitted character, 
its presence depends entirely upon the nature of the background upon which 
the insect lives and it is a character that may be acquired in a couple of days 
(see especially Expts. IV and VIII). This phenomenon should be borne in 
mind by investigators engaged in the study of heredity. 
4. THE RELATIVE PROPORTION OF THE SEXES. 
In Parasitology , x. pp. 114-115, reference was made to the relative pro¬ 
portion of the sexes in P. humanus encountered (a) naturally upon the host 
and (b) in broods raised experimentally, and it was stated that further enumera¬ 
tions were required before reaching final conclusions on the subject. An 
examination of Bacot’s hybrids of capitis and corporis has revealed the presence 
of a large number of hermaphrodites amongst them, a discovery that vitiates 
the figures cited ( loc. cit.) from that author. A detailed study of these and 
other hermaphrodites will form the subject of another paper by Dr Keilin 
and myself. 
ENUMERATION OF SEXES IN PEDICULI : 
(a) in insects encountered naturally upon the host. 
The following enumerations are based on specimens which have reached 
me from various parts of the world. The different lots contained numerous 
immature stages together with the adults. 
O © 
No. of lot 
Description 
Total adults 
c? 
? 
§ 
%$ 
273 
corporis, Sydney, N.S.W. 
196 
62 
134 
19 
68 
278 
,, Nairobi, B.E.A. 
364 
141 
223 
1 
64 
279 
99 99 99 
350 
131 
219 
0 
63 
277 
99 99 99 
245 
95 
150 
2 
61 
274 
„ Sydney, N.S.W. 
103 
40 
63 
0 
61 
257 
,, Tanga, E.A. 
173 
71 
102 
2 
59 
236 
capitis + corporis, Nairobi 
358 
148 
210 
0 
59 
237 
ft 99 99 
214 
94 
120 
2 
56 
252 
corporis, Cambridge 
446 
220 
226 
0 
51 
208 
capitis „ 
208 
104 
104 
0 
50 
282 
99 99 
35 
6 
29 
0 
* 
209 
,, London 
39 
14 
25 
0 
* 
285 
,, Bogota, Colombia 
38 
7 
31 
0 
* 
Totals 
2769 
1133 
1636 
26 
59% 
* These figures alone are too small to afford a 
reliable percentage. 0-5 
% or over 
is re 
ckoned 
as 1 % so as to give *i round figure in the percentage column. 
( b) found in broods raised experimentally. 
The following enumerations are based on one lot (N. 265) of corporis 
raised in successive broods in Cambridge during August-October 1918 from 
a few parents kindly supplied by Mr A. Bacot. The breeding boxes contained 
black cloth, the insects were fed twice daily and maintained at 31° C. in the 
thermostat between feeds. 
