D. Keilin and G. H. F. Nuttall 
325 
increase in the size of the females and the number of eggs they laid, also that 
the insects became less active. 
On 14 xi. 1917, Mr Bacot sent us some living specimens (N. 248) of capitis 
that he had bred for two years in the laboratory and, on examination by us, 
they were found to possess characters that were intermediate between those 
of typical capitis and corporis respectively. 
On 22x1.1918, we received a further consignment (N. 287) of the same 
stock from Mr Bacot, his “1915 strain,’’ which we are at present breeding; 
the lice are in every morphological detail like corporis having lost all the 
supposedly “specific” characters of capitis. 
On the last-mentioned date, Mr Bacot likewise sent us (N. 288) a lot of 
capitis described as his “1915-17 strain,” because, owing to an accident, 
his 1915 strain had become mixed with a fresh 1917 strain. The mixed 
strain mostly resembled typical corporis , a few specimens only showing 
intermediate characters. 
We may add that Howlett (xi. 1917, p. 186) raised capitis upon his body 
and that of his Assistant in India, and that he found 75 per cent, of the 
F 2 generation, consisting of ca. 40 individuals, resembled corporis in “chitiniza- 
tion and colour,” and that the remainder would be regarded as aberrant 
forms of corporis. Whilst chitinization and colour are not distinctive for 
the two races of lice, it is possible that Howlett’s strain of capitis may also 
have undergone modifications in structure. 
As we see from the foregoing records, capitis bred for two years in boxes 
had mostly assumed the characters of corporis , whilst after three years they 
could under no circumstances be taken for anything but a pure strain of 
corporis. Without experiments wherein such modified “ capitis ” or typical 
“ corporis ” are raised under normal conditions upon the head, it is impossible 
to say how long a period must elapse before they will assume typical capitis 
characters. 
APPENDIX II. 
Evidence as to the opportunities for intermingling of capitis and corporis 
in nature. 
Capitis on the head and corporis on the body of one host. Although there 
is but one published record available to show how frequently man may be 
infested with both capitis and corporis, it proves sufficiently that he often 
harbours these lice simultaneously. An instance, in a woman, is cited by 
Nuttall (xi. 1917, p. 86), and such cases could easily be multiplied, especially 
if long-haired persons were chosen for examination, such individuals being 
much more prone to head-lice. 
Hase (1915 a, pp. 9-11), who examined about 1000 persons in Poland 
during the German occupation, supplies the following record of the prevalence 
of head-lice and body-lice among a poor and mainly Jewish population: 
