THE BIOLOQY OF WOOD-BORINQ TEREDINID MOLLUSCS
380
secretory cells, differing in size and staining properties, in both cerebral
and visceral ganglia but only one type has been noticed in the pedal
ganglia. The secretion is formed in four successive stages and the
material is transported by way of the axons.
13. The reproductive system
The gonads are symmetrical consisting of branching tubules which
when mature form creamy white masses opening separately into the
supra-branchial cavity by the gonopores through two short, wide ducts.
The position of the gonad varies in different species and, as Turner
(1966) states, " the position of the gonads appears to be primarily a
matter of available space." The main body of the gonads may be
posterior to the caecum as in Teredothyra matocotana, Nausitora fusticula and other species with a comparatively small caecum, or the gonad
may extend along the dorsal side of the caecum as in Nausitora dunlopei. The gonopore is invariably situated at the posterior end of the
pericardial cavity except in Kuphus.
I n sexually mature Nausitora hedleyi the gonads occupy almost the
entire available space within the mantle cavity and sometimes the
tubules of the gonad are so crowded as to press closely against the
neighbouring organs. I n ripe specimens collected during the breeding
season, the part of the body behind the caecum may appear swollen on
account of the great development of the gonad. The gonad is massive
in a mature animal where the weight of this organ alone may form
nearly half that of the entire animal. The gonad in Teredora princesae
is also very conspicuous extending beyond the caecum. I n mature
specimens the space behind the caecum between the gills is virtually
packed with follicles of the gonad. I n the disposition of the gonad in
relation to the visceral ganglion, T . princesae differs from N . hedleyi
where the entire gonad even in very long specimens lies anterior to the
visceral ganglion, with only the gonoducts passing beneath the ganglion
to open behind it into the epibranchial cavity. On the basis of available
information, tentative conclusions can be reached about the relation of
the reproductive system to other structures in the mantle cavity. While
the position of the gonopore is apparently constant, at the original site
of the gonadal primordium adjacent to the visceral ganglion, the rest
of the gonad extends according to the available space. I n T . princesae
the major part is distributed behind the visceral ganglion probably as
a result of the curious horse-shoe shaped bending of the appendix and
the consequent crowding of the organs in that region. In Teredo navalis
the follicles of the gonad are distributed in the region in front of the
visceral ganglion above the caecum. I n Bankia indica, while maintain-
380
secretory cells, differing in size and staining properties, in both cerebral
and visceral ganglia but only one type has been noticed in the pedal
ganglia. The secretion is formed in four successive stages and the
material is transported by way of the axons.
13. The reproductive system
The gonads are symmetrical consisting of branching tubules which
when mature form creamy white masses opening separately into the
supra-branchial cavity by the gonopores through two short, wide ducts.
The position of the gonad varies in different species and, as Turner
(1966) states, " the position of the gonads appears to be primarily a
matter of available space." The main body of the gonads may be
posterior to the caecum as in Teredothyra matocotana, Nausitora fusticula and other species with a comparatively small caecum, or the gonad
may extend along the dorsal side of the caecum as in Nausitora dunlopei. The gonopore is invariably situated at the posterior end of the
pericardial cavity except in Kuphus.
I n sexually mature Nausitora hedleyi the gonads occupy almost the
entire available space within the mantle cavity and sometimes the
tubules of the gonad are so crowded as to press closely against the
neighbouring organs. I n ripe specimens collected during the breeding
season, the part of the body behind the caecum may appear swollen on
account of the great development of the gonad. The gonad is massive
in a mature animal where the weight of this organ alone may form
nearly half that of the entire animal. The gonad in Teredora princesae
is also very conspicuous extending beyond the caecum. I n mature
specimens the space behind the caecum between the gills is virtually
packed with follicles of the gonad. I n the disposition of the gonad in
relation to the visceral ganglion, T . princesae differs from N . hedleyi
where the entire gonad even in very long specimens lies anterior to the
visceral ganglion, with only the gonoducts passing beneath the ganglion
to open behind it into the epibranchial cavity. On the basis of available
information, tentative conclusions can be reached about the relation of
the reproductive system to other structures in the mantle cavity. While
the position of the gonopore is apparently constant, at the original site
of the gonadal primordium adjacent to the visceral ganglion, the rest
of the gonad extends according to the available space. I n T . princesae
the major part is distributed behind the visceral ganglion probably as
a result of the curious horse-shoe shaped bending of the appendix and
the consequent crowding of the organs in that region. In Teredo navalis
the follicles of the gonad are distributed in the region in front of the
visceral ganglion above the caecum. I n Bankia indica, while maintain-