albumen gland resembles the hermaphrodite gland, that is to say it is a collection of small
lobules compressed together. The ducts of these lobules unite to form larger ducts, and
the albumen gland, regarded as a whole, is not a passage with glandular walls but an
accessory to the mucus gland, into the cavity of which it opens by a single duct. The
cells of the albumen gland are full of a secretion which takes a nuclear stain and hence
the nuclei of the cells are obscured in sections. (b) A portion composed of cells having
granular contents. In the figure this portion appears only at the point marked h, but it
extends behind the coils of the mucus gland shown in the figure until it almost reaches
the albumen gland. I t is not like that organ an accessory gland, but is a part of the
oviducal passage differing from the rest only in the character of its walls. I t probably
acts as a shell-gland which secretes a shell round each ovum separately, before the ova
are collected in groups and arranged in the string of mucus; I have not been able to
follow with any certainty the path of the ova in these devious passages, but it seems
reasonable to suppose that they first receive the secretion of the aibumen gland; then
pass through the shell gland, going from right to left across but behind the whole
glandular complex shown in Figure 7; and finally pass through the coils shown on the left
side of that figure to the external orifice. I t will be seen that this orifice lies near the
middle of the glandular complex considered as a whole, not at the end, so that the ova
must traverse the same distance more than once before they can reach it. (c) The mucus
gland proper, or convoluted uterus with glandular walls. This large and complicated
organ constitutes the major part of the anterior genital mass and falls into two portions,
of which that occupying the left side in the figure is considerably the larger. I t consists
of a coiled and flattened tube, which in places spreads out into wide but compressed
cavities similar to the spaces which may be left between- sheets of paper. In this
labyrinth the eggs are arranged in a string of mucus and along the whole length of the
string is attached a thin ribbon or lamina. The lower surface of this lamina is fixed to a
solid object when the eggs are laid so that the string can float without wandering from
its position. The walls of the mucus gland are formed of glassy cells with small but
distinct nuclei.
Although the reproductive organs of AEolids are described in most text-books as
diaulic, it will be seen from the above description that they are triaulic; for I
understand the essence of the diaulic arrangement to be that the hermaphrodite duct
divides into two parts only, namely, (a) a male channel, (b) a female channel,
serving for both fertilization and oviposition, and bearing the spermatotheca as an accessory
diverticulum. This is the arrangement commonly illustrated in text-books by figures of
Helix pomatia or H. hm'tensis. But in the triaulic arrangement the hermaphrodite duct
gives rise to three tubes1: (a) male; (&) a channel for fertilization; (c) a channel for
1 This is a convenient description of the structure as it exists, but its origin may be not that the
hermaphrodite gland is split into three, or the female branch into two tubes, but that the spermatotheca
sends off an additional duct to the upper oviduct. Some aspidobranch Mollusca (such as
Nerita and Neritina), though dicecious, have the female genitalia- divided into two tubes, as in the
triaulic Nudibranchs, for copulation and oviposition. In Septaria the female genitalia appear to be
triaulic by themselves (a greater complication than is known to exist in any Nudibranch), and to
have, besides the copulatory and ovipository orifices, a third orifice of unknown functions.
oviposition. These three channels exist in 2E. papillosa (which is not in this respect constructed
like Helix pomatia), but they differ from the corresponding organs of Doris in
the following points: (1) The vaginal and oviducal passages unite in a common atrium
and are not visible as separate openings from the exterior. (2) There is only one
spermatotheca, and though it is folded on itself the division appears to have no structural
importance. I t is possible, however, that the bulges often noticeable near the base may
perform the same functions as those attributed to the second spermatotheca of Doris,
that is to say, the spermatozoa when first received are probably combined in bundles or
embedded in mucus, and it may be that when isolated and cleaned they collect in the bulges
ready to descend into the oviduct. (3) "Whereas in Doris both spermatothecas lie between
the oviduct and the external orifice* in 2E. papillosa the duct from the exterior joins the
oviduct, and close to this point of junction the spermatotheca arises out of the oviduct.
One would suppose that this position makes it more difficult for the spermatozoa to reach
the spermatotheca, but when they once have reached it they are very conveniently
situated for fertilizing the ova as they pass down the oviduct. I t is almost certain that
the spermatozoa are detained for some time in the spermatotheca, and this seems to imply
that they are expelled at the proper time by some movement of this organ. Probably
the movement of the oviduct which causes the ova to descend also provides a stimulus
which causes the muscular walls of the spermatotheca to contract.
I t follows from the above that the JEolids and their allies are not diaulic as a class.
Many distinguished authorities have stated the contrary but neither their descriptions nor
their figures are sufficient to prove this generalization. The latter, numerous as they are,
rarely show the relations existing between the various parts of the genitalia, but represent
either isolated organs or else the genital mass in its natural compressed condition in which
the connection between the various tubes is rarely plain. But Trinchese’s figures of
Spurilla neopolitana,1 though not very clear, appear to indicate a structure like that here
described for JE. papillosa. There is little evidence to show how far this structure is
common to Solids, and much minute investigation is necessary before any general statement
can be made. According to Hancock and Embleton the disposition of the organs in
Facelina cororiata is similar though not identical, but I have not been able to verify their
statements either by dissection or by microscopic sections.2 It seems probable that the
less specialized forms in both the Clado- and Holohepatica (e. g. Dendronotus and Melibe in
the one, Tritonia in the other) are truly diaulic, but that with increased specialization the
triaulic condition is more or less completely developed.3
1 Anatomia e fisiologia della Spurilla neapolitana Bologna, 1878, PI. v, fig. 27.
8 The investigation of the reproductive apparatus in ASolids offers great difficulty. Except in
large animals the ducts are so small and fragile that their relations cannot be determined by dissection.
On the other hand, the mucus and albumen glands when prepared for sectioning become so hard that
it is sometimes impossible to cut them, and, even in the most favourable conditions, many sections
become distorted or spoilt.
s. I t is only just to Bergh to say that he defined diauly and triauly as the presence of two or three
external openings respectively. In that sense all known Cladohepatica appear to be diaulic. But
other authors rightly emphasize the bifurcation or trifurcation of the hermaphrodite duct as the
important point.