In my previous paper on the body louse (1916) many points of morphological interest were necessarily left in abeyance and mention was made that certain statements in it were open to correction. Further work has rendered correction possible. While working in France, to ascertain whether Pediculus humanus was a carrier of the spirochaete of Weil's disease, opportunity was taken to investigate those organs of the louse in which the spirochaete might lodge and the afferent and efferent channels through which it might pass. The enquiry did not demonstrate the presence of the spirochaete in the body louse, but incidentally a detailed knowledge of the mechanism of feeding was obtained and is here presented. Since the main conclusions of this paper were reached (December, 1916) I have read Harrison's paper, “A Preliminary Account of the Structure of the Mouth-Parts in the Body-Louse,” and while much of the following verifies his statements, we differ on certain important points regarding the structure of the mouth-parts and musculature.