G. H. F. Nuttall 
299 
apparatus and considers that the basal plate is probably derived from 
two longitudinal apodemes upon whose posterior ends articulate the 
two parameres. He prefers, however, to call Mjbberg’s preputial sack 
“the mesosome.” The large and extrusible end of the latter is said to 
be continuous with the ductus ejaculatorius, and distally it bears the 
penis, with frequently a splint on each side called the telomere, and 
beneath, the hypomere (terms applied, according to Cummings, by 
Waterston, 1914, Ann. S. Afric. Museum, x, 279, to Philopterid forms). 
At the proximal end are the endomeres, usually strongly chitinized 
bands or rods, one on each side, supporting the membrane of the sack 
of which they are only local thickenings. Cummings notes a suture in 
the middle line of the basal plate. 
Judging from the instructive"figures whereby Cummings illustrates 
these structures in different forms {Linognathus, Trichodectes, Goniodes, 
etc., but not in Pediculus) it appears to me that in Pediculus, Mjbberg’s 
parameres are the parameres + endomeres of Cummings. Adopting 
for the moment the nomenclature of Cummings, I believe that in 
Pediculus we have a partial fusion of. the endomeres distally and that 
they exceed the parameres in length, the latter being fused laterally 
to the endomeres and thus appearing merely as two small points (see 
PI. Ill, figs. 1, 2). Cummings illustrates the extruded preputial sack 
in three species belonging to different genera, and it is clear that the 
function of this organ, though it varies in form in different species, is 
similar to that we shall describe in this paper for Pediculus. 
Although not wishing to detract from the importance of the con¬ 
tributions of Mjoberg and of Cummings, neither of them afford evidence 
of these authors having studied the apparatus they describe other than 
in caustic potash preparations, for only the chitinous structures are 
referred to. The mechanism of the apparatus therefore remains to be 
described and an effort to do so is made in this paper. 
The musculature of the male copulatory apparatus has received 
scant attention. Except for the protractor muscles which have their 
origin at the posterior and postero-ventral portion of the body wall and 
run forward to their insertions upon the margin of the basal plate, the 
musculature of these parts has not hitherto been understood. In 
addition to the protractor muscles just mentioned, Landois (1865, 
pp. 53-54) refers to retractors inserted dorsally upon the plate and 
arising from the inside of the last segment; he does not state whether 
they arise dorsally or ventrally upon the segment. Pawlowsky (1907, 
pis. IV, VI, figs. 19,29-33) describes circular muscles about the ejaculatory 
Parasitology ix 20 
