of _I. Cumingii_ be the
male of that species, then unquestionably we have in _I. quadrivalvis_ a
male, complemental to an hermaphrodite,--a conclusion, as we have seen,
hardly to be avoided in the genus Scalpellum, even if we trust
exclusively to the facts therein exhibited.

With respect to the positions of the parasitic males, in relation to the
impregnation of the ova in the females and hermaphrodites, it may be
observed that in the two male Iblas, the elongated moveable body seems
perfectly adapted for this end; in the males of the first three species
of Scalpellum, the spermatozoa, owing to the manner in which the thorax
is bent when protruded, would be easily discharged into the sack of the
female or hermaphrodite; this would likewise probably happen with the
complemental male of _S. rostratum_, considering its position within the
orifice of the capitulum, between the mouth and the adductor scutorum
muscle. The males of _S. Peronii_ and _villosum_ being fixed a little
way beneath the orifice of the sack, below the adductor muscle, are less
favorably situated, but the spermatozoa would probably be drawn into the
sack by the ordinary action of the cirri of the hermaphrodite, and
therefore would at least have as good a chance of fertilising some of
the ova, as the pollen of many dioecious plants, trusted to the wind,
has of reaching the stigmas of the female plants. Regarding the final
cause, both of the simpler case of the separation of the sexes,
notwithstanding that the two individuals, after the metamorphosis of the
male, become indissolubly united together, and of the much more singular
fact of the existence of Complemental males, I can throw no light; I
will only repeat the observation made more than once, that in some of
the hermaphrodites, the vesiculae seminales were small, and that in
others the probosciformed penis was unusually short and thin.

Viewing the parasitic males, in relation to the structure and appearance
of the species to which they belong, they present a singular series. In
_S. Peronii_ and _S. villosum_, the internal organs have the appearance
of immaturity; the shape of the capitulum is specially modified for its
reception between the scuta of the hermaphrodite, and several of the
valves have not been developed. This atrophy of the valves, is carried
much further in _S. rostratum_. In Ibla, many of the parts are embryonic
in character, but others mature and perfect; some parts, as the
capi