D. Keilin and G. H. F. Nuttall 
323 
like or flattened chitinous structures occurred about the peri-buccal region. 
These structures are unquestionably hypertrophied hairs, for they occupy 
corresponding positions to such hairs, show transition forms, and communicate 
at their base with a terminal nerve ganglion (Text-fig. 28 c). This abnormality 
may have arisen prior to the last ecdysis. It is noteworthy that it was observed 
only in two specimens of one family. 
Malformations due to accident. 
As in all insects, malformed limbs may arise owing to their premature 
hardening whilst in a confined space, for instance when ecdysis is unduly 
prolonged. Pediculi with truncated limbs are frequently encountered, one or 
more legs, or an antenna being deficient. This is due to accident. Repeated 
and varied experiments have shown that amputated limbs are not regenerated. 
III. 
CONCLUSIONS. 
I. Hermaphroditism. 
The following conclusions are based on the study of a very large material, 
155 hermaphrodites, which were examined in detail and yielded a complete 
series of forms beginning with those of male type and ending with those of 
female type, the co-existing characters of both sexes being present to a varying 
degree. 
All of our hermaphrodites can be classified as belonging to Friese’s “Mixed 
Gynandromorphs,” and they include representatives of Cockayne’s three 
groups that are described as Genetic, Primary Somatic, and Secondary Somatic 
Hermaphrodites. 
None of our specimens accord in any way with “halved gynandromorphs,'’ 
but they resemble the “intersexual” forms of Goldschmidt 1 . 
The state of development of the gonads in our hermaphrodites is not 
in accord with that of the secondary sexual organs. 
Hermaphroditism in Pediculus humanus is often accompanied by secondary 
malformations, viz., fragmentation of the dorsal bands, disorientated proli¬ 
feration of the genitalia of one sex, and various invaginations, devaginations 
and prolapses of the genitalia. These prolapses, in the male organs, are due 
to atrophy of the retractor muscles and basal plate, whilst in the female 
organs the prolapses are either due to abnormal development or coital 
traumatism. 
The anatomical structure of our hermaphrodites indicates that they may 
be either sexually non-functional or functional, serving, in the latter case, 
as males or females in respect to copulation. 
The material studied by us consists of two classes, (a) that obtained 
1 Reference on p. 313. 
