D. Keilin and G. H. F. Nuttall 
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some reason, does not take place uniformly, we can understand why the 
organs that are formed in the folds of the developing tissue may not expand to 
their normal form and remain imprisoned within the body of the insect. The 
simultaneous growth of the organs of both sexes in a hermaphrodite suffices 
to explain these irregularities of proliferation. 
The devaginations, frequently observed by us in the hermaphrodites, differ 
according to the character of the specimen. In female organs two kinds of 
devaginations occur, (a) natural devagination due to malformation in the 
course of development, (b) traumatic devaginations or prolapses, which we 
attribute to injury during coitus, this, at times, leading to rupture of the 
vagina followed by expulsion of the internal genital organs. In male organs 
we have to consider what takes place normally. In Pediculus, and certainly 
in some other Anoplura, the male genital armature is retracted into the 
body when at rest, but becomes extruded in the form of a sack surmounted 
by a penis during copulation. In Bacot’s material, we found a number of 
hermaphrodites that had died with their male genitalia extruded, this being 
attributable to one of three causes: (a) the sack having been extruded during 
ecdysis and the atrophied retractor muscles not permitting of its retraction, 
(b) the sack having been extruded during coitus and not having been retracted 
for the reason just stated, ( c ) the sack having been extruded owing to the 
pressure exerted by the proliferation of the female genital organs. The last 
explanation appears inadequate to us because we have seen specimens replete 
with eggs (Specimen 13, PI. XIV) in which the male genitalia are not extruded. 
Whatever the cause of the extrusion may be, the inability to retract the 
sack (vesica penis) is certainly due to atrophy of the retractor muscles, which 
in all such cases are correlated with an atrophic condition of the basal plate 
upon which the retractors are inserted. 
In no case were the male and female genitalia situated to the right or 
left of each other as in halved or lateral gynandromorphs. 
(B) Internal sexual organs. 
The state of preservation of the material studied only permitted us to 
examine the internal organs in twelve specimens. These, however, showed 
certain variations in the degree of development attained by the male and 
female organs of which the following may serve as examples: 
(1) A c£ contains 4 well developed testes, the remaining male organs being 
normal. There are also two large eggs present, but they have no means of 
exit from the body. 
(2) A (Specimen 12, PI. XIII, described on p. 290) contains 3 testes 
widely apart, with all the other male organs normal and but slightly displaced. 
Two large eggs and some young ovules are present but have no means of 
exit from the body, the secondary female sexual organs being obsolete. 
(3) A $ (Specimen 13, PI. XIV, described on p. 290) contains 1 testis, 
