The great importance of lice as parasites and vectors of disease in man led one of us (Nuttall), soon after the outbreak of the Great War, to undertake a detailed study of these insects. It was known, prior to the war (1909–14), that lice transmit typhus and relapsing fever and during the war (1917–18) it was established that they also serve as vectors of trench fever. Beginning with February 1917, a number of papers dealing with various aspects of the louse problem were published in Parasitology (see vols. X–XIII), the study of their structure, systematics and biology being actively pursued whilst the best methods of combating them were sought for with a view to aiding the armies in the field. Of these papers, that dealing with the structure and function of the genitalia in Pediculus (II, 1917) bears directly on the subjects to which this Iconography relates.