390
N. BALAKRISHNAN NAIR AND M. SARASWATHY
ing the position of the gonopore near the visceral ganglion, the gonad
extends not only anteriorly but some distance posteriorly as well. This
can be explained on the basis of the position of the visceral ganglion, in
this species placed approximately a third of the distance from the
distal tip of the caecum. In N . hedleyi the distribution of the gonadial
follicles departs from the typical condition stretching for a considerable
distance between the caecum and the gonopore. In T . princesue this is
short as in other shipworms and opens into the supra-branchial chamber
and the follicles of the gonad spread above the appendix and beneath
the ctenidia for some distance anteriorly as well. According to Sigerfoos
(1908), the real " gonoduct " is remarkably short, formed as an ectodermal invagination soon after settlement the duct not breaking
through till sexual maturity.
In Teredo furcifera the gonadial follicles even extend into the connective tissue of the mantle in certain regions. The major part of the
gonad spreads over the caecum, the maturing follicles filling up the
available space below the pericardium and posteriorly dilating so as to
push aside the pericardium with its contained auricles. The gonoducts
lie on the ventral side of the visceral ganglion.
IV. THE SEXUAL PHASES
As in many other Bivalvia (Fretter and Graham, 1964) sexual conditions vary widely in the Teredinidae. In Teredo norvegica Yonge
(1926b) noticed that the males were generally the smaller while the
presence of two specimens containing both ova and spermatozoa indicated that this species is protandrous. Sigerfoos (1908) had already
noted hermaphrodites among young specimens of Bankia gouldi and
suspected the occurrence of protandry. Coe (1933-41) elucidated the
sequence of sexual phases based on histological studies in Teredo,
Bankia and Lyrodus. I n the first paper (1933) he revealed that T .
navalis is a protandric hermaphrodite. The primary gonad contained
both oogonia and spermatogenic cells, all individuals passing through
an initial functional male phase and most of them later transforming
into functional females with a small number persisting as true males.
After assumption of the defhitive female phase, no evidence of a second
sex reversal was noticed. Subsequently Coe (1934) showed the existence
of a great disparity in sex ratios at different seasons of the year. (A
change from the female phase to a second male phase was also reported
by Coe (1934), according to whom animals which complete both sexual
phases before the winter may repeat the succession of sexual phases in
the next year.) Grave and Smith (1936) showed that in Teredo functional males constitute 30-50% of the adult population with a pre-
N. BALAKRISHNAN NAIR AND M. SARASWATHY
ing the position of the gonopore near the visceral ganglion, the gonad
extends not only anteriorly but some distance posteriorly as well. This
can be explained on the basis of the position of the visceral ganglion, in
this species placed approximately a third of the distance from the
distal tip of the caecum. In N . hedleyi the distribution of the gonadial
follicles departs from the typical condition stretching for a considerable
distance between the caecum and the gonopore. In T . princesue this is
short as in other shipworms and opens into the supra-branchial chamber
and the follicles of the gonad spread above the appendix and beneath
the ctenidia for some distance anteriorly as well. According to Sigerfoos
(1908), the real " gonoduct " is remarkably short, formed as an ectodermal invagination soon after settlement the duct not breaking
through till sexual maturity.
In Teredo furcifera the gonadial follicles even extend into the connective tissue of the mantle in certain regions. The major part of the
gonad spreads over the caecum, the maturing follicles filling up the
available space below the pericardium and posteriorly dilating so as to
push aside the pericardium with its contained auricles. The gonoducts
lie on the ventral side of the visceral ganglion.
IV. THE SEXUAL PHASES
As in many other Bivalvia (Fretter and Graham, 1964) sexual conditions vary widely in the Teredinidae. In Teredo norvegica Yonge
(1926b) noticed that the males were generally the smaller while the
presence of two specimens containing both ova and spermatozoa indicated that this species is protandrous. Sigerfoos (1908) had already
noted hermaphrodites among young specimens of Bankia gouldi and
suspected the occurrence of protandry. Coe (1933-41) elucidated the
sequence of sexual phases based on histological studies in Teredo,
Bankia and Lyrodus. I n the first paper (1933) he revealed that T .
navalis is a protandric hermaphrodite. The primary gonad contained
both oogonia and spermatogenic cells, all individuals passing through
an initial functional male phase and most of them later transforming
into functional females with a small number persisting as true males.
After assumption of the defhitive female phase, no evidence of a second
sex reversal was noticed. Subsequently Coe (1934) showed the existence
of a great disparity in sex ratios at different seasons of the year. (A
change from the female phase to a second male phase was also reported
by Coe (1934), according to whom animals which complete both sexual
phases before the winter may repeat the succession of sexual phases in
the next year.) Grave and Smith (1936) showed that in Teredo functional males constitute 30-50% of the adult population with a pre-