l appendages in the _I.
quadrivalvis_ attain a greater length than in any other species of the
family, being four times the length of the pedicels of the sixth cirrus.
A far more important peculiarity is the fact of the oesophagus, in both
species, running over or exteriorly to the adductor scutorum muscle,
instead of, as in every other species, close under this muscle. I took
great pains in ascertaining the truth of this singular anomaly: the
course of the oesophagus is approximately represented in Pl. IV, fig. 8
_a'_ by faint dotted lines. The stomach has no caeca; the biliary folds
are longitudinal; there is a marked constriction at the line
corresponding with the junction of the thorax and prosoma. There are no
filamentary appendages.

The generative system gives the chief interest to this genus. We here
first meet with Males and Females distinct; and, within the limits of
this same restricted genus, the far more wonderful fact of
hermaphrodites, whose masculine efficiency is aided by one or two
Complemental Males. The complemental and simple males closely resemble
each other, as do the female and hermaphrodite forms; but under the two
following species I enter into such full and minute details on these
remarkable facts, that I will not here dilate on them. I may add that,
at the end of the genus Scalpellum, I give a summary of the facts, and
discuss the whole question. The penis (Pl. IV, fig. 9 _a_) in the
hermaphrodite, _I. quadrivalvis_, is singular, from the length of its
unarticulated support, and from the distinctness of the segments in the
articulated portion.

As ovigerous fraena occur in the usual place in _I. quadrivalvis_, though
much smaller than in any other species, I have no doubt that they occur
in _I. Cumingii_, although I failed in observing them. The glands on the
margin, in _I. quadrivalvis_, are singular, from not being borne on a
long, hair-like footstalk.

_Affinities._--Ibla, though externally very different in appearance from
Scalpellum, is more nearly related to that genus than to any other; in
both genera some species have the sexes separate, the imperfect males
being parasitic on the female, and other species are bisexual or
hermaphrodite, but aided by parasitic complemental males. In Scalpellum,
again, the oesophagus pursues a sinuous course, resembling that in Ibla,
though it does not pass exteriorly to the adductor scutorum muscle. The
disc of the prehensile antennae of the larva, i