280 
Hermaphroditism etc. in Pediculus 
us from different parts of the world, we came upon (c) further specimens in 
a large material received from Mr A. Bacot, Entomologist to the Lister 
Institute. 
In describing material ( a ) and (b) above specified, we were guided by 
morphological considerations in respect to the sequence in which the various 
abnormalities are described, whilst the order in which (c) Bacot’s material 
is treated corresponds to that of the various families and generations in 
which the specimens were contained, all being derived from crosses between 
capitis and corporis, some raised up to the third generation in the laboratory. 
The foregoing material permits us to describe a complete series of 
hermaphrodites, to explain certain anomalous structures in them, and to 
advance a reasonable hypothesis as to the origin of hermaphroditism in 
Pediculus humanus. Our studies have opened up a fruitful field of investiga¬ 
tion bearing on the sex problem. 
Acknowledgments. 
We have pleasure in acknowledging the invaluable assistance we have 
received from Mr A. Bacot, who placed his material at our disposal for 
purposes of study, and on several occasions sent us living specimens of 
» 
P. humanus, both capitis and corporis, wherewith to conduct experiments. 
We are also indebted to the Hon. H. Onslow for kindly directing our attention 
to some of the recent literature relating to gynandromorphism. 
Sexual dimorphism in Pediculus humanus. 
Before proceeding to the consideration of the 155 hermaphrodites we 
have studied, it is necessary, in the first place, to dwell briefly upon the 
characters that differentiate the sexes in normal lice: 
Primary and secondary sexual organs. 
MALE (Text-fig. 1): Internal sexual organs. The male possesses two pairs 
of testes, each testis being piriform in shape, the pair approximating to each 
other basally where they open into a common vas deferens (v.def.). The vasa 
deferentia, leading from the paired testes on each side, terminate in corre¬ 
sponding branches of the forked vesicula seminalis (v.sem.), the vesicula in 
turn leading to the ductus ejaculatorius ( d.ej .). Where the latter joins the 
vesicula, this is bent abruptly backward, so that the duct and vesicula lie 
parallel to each other in the median line. 
External genitalia. When devaginated, the copulatory apparatus consists 
of a chitinous, dentate vesicula, a penis protruding dorsally between the 
branches of the dilator which hinges proximally upon a basal plate. The 
protruding penis is borne laterally upon the vesica penis. When retracted, 
these parts can be more or less distinctly seen by transparency. The pointed 
