144 
Purported New Species , etc. 
studies require the use of other methods than the usual one of treating speci¬ 
mens with caustic potash and mounting them in balsam. Fahrenholz’s 
purported species of Pediculus , i.e. schaffi, lobatus and oblongus ( = assimilis) 
were degraded by me (Ibid. pp. 334-340), the first to a race of P. humanus , 
whilst the others were merely regarded as probably forms of the variable race 
capitis. Of Fahrenholz’s varieties of “P. capitis ,” i.e. maculatus, angustus and 
marginatus (since raised to the rank of sub-species by that author), I ventured 
“to assert that these names will not stand and that they will fall into the 
synonymy of P. humanus ,” also that they “are surely based on faulty ob¬ 
servation.” Already in an earlier paper (n. 1919, p. 208), referring to the three 
above-mentioned varieties, I wrote: “Judging from Fahrenholz’s other 
publications to which I shall refer elsewhere (meaning here), this author has 
also in this instance merely burdened science with three names which will fall 
into the synonymy of Pediculus humanus .” That these comments were 
justified is proved by the following detailed criticism dealing with (a) the 
measurements, (6) morphology and (c) pigmentation of Pediculus and their 
bearing on the forms which Fahrenholz has attempted to define. 
(a) Measurements of Pediculus. 
There are certain sources of error that cut at the base of all measurements 
made on lice, and these require consideration because they have been widely 
ignored: (a) When lice die and dry up, the soft parts of the integument shrivel 
so that the insects shrink considerably. The antennae become shortened, the 
hard parts, this being especially evident in capitis, becoming partly telescoped 
into each other. The neck-like portion of the head is retracted into the thorax, 
the abdomen collapses and may shorten greatly, (b) When dried lice are 
placed in water their soft parts imbibe the fluid and the body resumes its 
normal contour, but by placing them afterwards in alcohol whose strength 
is gradually increased, such previously dried specimens may be made to 
retain their normal external form, (c) When dried specimens are placed in 
10 per cent, caustic potash their bodies imbibe fluid and become swollen to 
the limit of their capacity if the exoskeleton is uninjured, (d) When fresh or 
dry caustic-treated specimens are cleaned and mounted in balsam, they 
frequently collapse again more or less provided extra precautions are not 
taken; therefore measurements made on balsam-mounted specimens are 
fallacious in most cases. 
When living or well preserved lice are examined, it is evident ( e ) that the 
amount of food they have imbibed alters their dimensions and (/) that the 
number of eggs contained in the body of the female distinctly alters the length 
and width of the abdomen. Moreover, (g) the head protrudes more from the 
body of fully fed lice than from those that are unfed or but partly fed. 
As an example of the effect of feeding upon the body-length I cannot do 
better than cite an observation by Sikora (ix. 1917, p. 276) who measured 1 
two females before and after feeding, the result being more striking in the 
