near the distal end and joins the oviduct. The neighbourhood of this junction probably
serves as a fertilization chamber. A pouch which is apparently assigned to this purpose
exists in allied forms (e. g. Polycera), but has not been found in JD. tuberculata. We thus
see how the spermatozoa introduced by the copulatory orifice reach the ova, but what are
the functions of the spermatotheca and spermatocyst ? The former probably acts as a
bursa copulatrix, and when the genitalia are protruded becomes accessible to the intro-
mittent organ, thus affording a first resting-place for the spermatozoa. I t is found1 to
contain not only free spermatozoa, but spermatozoa in packets and also detritus. The
spermatocyst, on the other hand, contains only free spermatozoa: it has never been found
full when the spermatotheca is empty, but has occasionally been found empty:when there
were some contents in the spermatotheca. More usually both organs arë full or both
empty. It therefore seems likely that the spermatozoa are received by the spermatotheca
in packets, and that when the envelopes break up they escape and migrate to the
spermatocyst. Here they await the descent of the ova into the oviduct. I t is probable
that most Nudibranchs, though hermaphrodite, exercise their sexual 'functions alternately
and are protandrous. »In the pairing season both individuals act as males and afterwards
begin to produce ripe ova. Hence the spermatozoa have to be stored for a few days or
hours until the oVa are ready. But this explanation, though plausible, requires to be
confirmed by further observation.2 I t has also been suggested that the function of the
spermatocyst may be to supplement cross-fertilization (undoubtedly the normal method in
Dm-is) by self-fertilization. According to this hypothesis its contents would consist of
spermatozoa which have passed to it from the hermaphrodite ampulla through the oviduct
and may be returned to the oviduct again.
The oviduct with its accessory organs forms both in its flattened and in its distended
condition a mass of tubules and cavities most difficult to unravel _or follow. Its complexity,
though astonishing, is not unnatural if we consider that it can secrete an egg-ribbon
fifteen inches long and three-quarters of an inch wide. I t clearly comprises a powerful
secreting apparatus and a most devious channel within whose windings the various secretions
are poured on the eggs; the difficulty is to say which tubes are, strictly speaking,
parts of the oviduct (that is, the channel followed by the egg) and which belong to glands
accessory to the oviduct and opening into its sides. The apparatus must fall functionally
into five parts, for the eggs undergo five operations within i t : they are fertilized and they
receive successively (1) a coating of albumen, (2) an egg-shell, (3) a coating of mucus
which combines them into a string, and (4) a second coating of mucus which arranges
the string in a ribbon. But morphologically these parts are not clearly separable. I t can
only be said that the portion known as the albumen gland is yellower than the rest and
denser, that is to say formed of smaller tubes. I t is definitely a gland and opens into the
distal end of the oviduct, though this position is generally obscured by the fact that it is
partly surrounded by the coils formed by the rest of the apparatus.
1 These observations have been made on many Dorids, but they have not all been verified for
-D. tiiberculata or for any single species. •
8 E.g. to show at what periods the male and female products ripen and whether both individuals
spawn as the result of a single act of pairing. It is certain that both spawn subsequently to pairing,
but equally certain that one individual sometimes pairs again before spawning.
Among those Dorids which have been adequately described, the structure of the ovi-
ducal branch is simplest in Polycera quadrilineata,1 a common British species. In this
animal there is a distinct spherical swelling in the oviduct, which doubtless acts as a
fertilization chamber (see Text-figure 5). From it the oviduct issues as a cylindrical tube
and receives the ducts of the albumen gland, along (or through) a portion of which it
passes (ƒ). I t then emerges again as a cylindrical tube, and it is probable that here
the walls of the tube secrete the egg-shell. The portions of the oviduct mentioned
up to now can be clearly distinguished from the mucus or nidamental portion which
follows. It has roughly the shape of a letter U (</). The eggs pass down and up the
left and right limbs of the letter, but the space between the limbs is not blank but filled
by two membranes enclosing a flattened cavity which communicates all round with the
oviduct,2 or, in other words, its edge is inflated into the tube forming the oviduct. In
the left limb of the U the tube is convolute. In the right it is broader and straight. From
this broad part a short tube runs to the external orifice of the oviduct (h).
The structure found in D. tuberculata is essentially the same as that described above,
but the different organs are combined in one complex where they can with difficulty be
distinguished,3 and the coils of the oviduct are greatly increased. No investigator has
discovered a distinct fertilization chamber, but a flat cavity corresponding to that
described above is found in the interior of the mucus gland. The terminal portion of the
oviduct (between the mucus gland and the exterior) is strong and laminated internally.
It is to some extent extruded during egg-laying when it probably acts as an ovipositor
and helps to form the shape of the egg-ribbon.
The complicated organ described above is here called mucus gland in conformity with
the usage of several authors. I t is also sometimes termed nidamental gland inasmuch as
its principal function is to produce the nidamental ribbon in which the eggs are embedded.
But though these designations correctly describe some of its principal functions, it may be
questioned if it would not on the whole be better to give it the name of uterus, since it is
a cavity, continuous, though of very complicated shape, within which the ova are fertilized
and prepared for expulsion in the form of eggs with suitable coverings.
The organ here called ampulla of the hermaphrodite gland is often found full of
spermatozoa, and there is reason to believe that it acts as a male receptaculum seminis which
retains the spermatozoa and does not allow them to pass into the vas deferens until they
are wanted. It may on occasion perform the same office for the unfertilized ova, but there
appears to be no record of its being found filled with them, and if the account given above
of the successive male and female phases is correct there is no reason to collect and hold
back the ova. If they descend as they ripen and provoke the secretions of the glands as
they pass, they will take their places naturally in the nidamental ribbon.
1 See H. Pohl, Über den feinem Bau des Genitalsystems von Polycera quadrilineata, Halle-a-S.,
1905.
It also communicates directly with the albumen gland through a small tube.
8 A simpler form of the complex is described and figured for Discodoris vonjheringi by MacFarland,
Opisthobranchiata of Brazil, 1909, pp. 79—82.