G. H. F. Nuttall 
341 
to corporis) has (i) the head shorter and blunter; (ii) the thorax broader 
anteriorly (Neumann, 1910); (iii) the legs shorter and stouter; (iv) the gono- 
pods blunter; (v) the chaelotaxy different; (vi) the egg smaller (Fahrenholz, 
1912, and others). Of these differences, that exhibited in the legs generally 
holds for typical head-lice, but none of the others are constant, as I have firmly 
convinced myself after examining a large material. Otherwise typical capitis 
may possess gonopods as pointed as in corporis and vice versa. Whilst Fahren¬ 
holz states that the chaetotaxy in corporis is characterized by fewer and smaller 
hairs upon the ventral surface of the abdomen (he illustrates this by compara¬ 
tive figures), the examination of his figures, or of actual specimens, proves 
that the hairs merely appear fewer in corporis because its body surface is 
larger (stretched) and the hairs consequently further apart. In justice to 
this author, his remark should be cited that he was “much disappointed” not 
to find a greater difference in the chaetotaxy. Fahrenholz ignores the state¬ 
ments of (i) Enderlein (1905) that he could find no difference in the chaetotaxy 
although he considered the two forms distinct species, and (ii) Neumann (1910) 
that the chaetotaxy is variable, which I contest if the statement applies to 
the number of hairs in this situation, where the number is fairly constant, 
though the hairs certainly vary in length both in capitis and corporis. The 
point made by Sikora (ix. 1917) that the thumb differs in the two forms, does 
not stand critical examination. In typical capitis , derived especially from 
African negroes, I find the chitinization most pronounced, this rendering the 
insects tougher, but intermediate degrees of chitinization occur leading down 
to the thinner exoskeleton of corporis. According to Landois (1865a, p. 494) 
the ventral abdominal muscles differ in female capitis and corporis ; this 
requires investigation. 
False statements . Piaget (1880, p. 619) asserted that capitis differs from 
corporis in having (i) no thoracic spiracles, (ii) seven abdominal segments 
and five pairs of abdominal spiracles, instead of eight and six respectively. 
These false statements, based on inaccurate observation, would need no 
comment but that one or the other have been cited in all innocence by 
Fahrenholz (1912) and Alessandrini (1916) in support of their contention that 
capitis and corporis constitute distinct species. 
Differences inconstant. All of the differences that earlier writers sought to 
establish between capitis and corporis, were dismissed as inconstant by Schjodte 
(1864) and Neumann (1910), except perhaps the deeper incisions between the 
abdominal segments in capitis. This difference I find cannot be relied on for 
it is likewise inconstant. Therefore, whilst there is no difficulty in referring 
a typical form either to capitis or corporis, there remains no constant morpho¬ 
logical difference between the two for they are linked together by all shades 
of intermediate forms passing through almost imperceptible gradations in 
size, general shape and details of structure. Pigmentation, being entirely 
dependent on the colour of the background (vide Nuttall, n. 1919, pp. 206-219), 
does not constitute a difference. 
