THE BIOLOGY O F WOOD-BORMQ TEREDINID MOLLUSCS
391
ponderance of functional males in young populations. Later a greater
part of the individuals were found to produce eggs, these females having
the ability to revert to the male phase. They also found that the transformation from female to male phase may occur abruptly during the
breeding season as well as during the recuperation period and that
gametes of both types capable of self fertilization may be produced in
the same follicle. Coe (1936) showed the existence of a sequence of
functional male and female phases in Teredo navalis-an initial functional male phase followed by a female phase, this often followed by a
second male phase and sometimes by a second female phase. Some
individuals remained in their first male phase for a long time or even
indefinitely and these he named as true males. Coe (1941) later demonstrated protandry with a strong tendency towards rhythmical change of
functional male and female phases in the larviparous Teredo diegensis
and in the oviparous Bankia setacea. He came to the conclusions that
(1) in Teredo diegensis functional hermaphroditism is common without
any sharp demarcation of the sexual phases ; ( 2 ) in T . navalis functional
hermaphroditism is not unusual, although the gonads are histologically
ambisexual during the change of sexual phases ; (3) in Bankia setacea
functional hermaphroditism occurs occasionally in the primary male
phase but subsequent sexual phases are well defined and there is often
a resting stage between them. Grave (1942) subsequently confirmed
Coe’s data on the recurrent functional sex inversion in Teredo navalis
but objected to his interpretation that Teredo is essentially or principally
a protandric hermaphrodite. More recently Ganapati and Nagabhushanam (1954,1959), and Nair (1956) have shown similar sex changes
in Teredo navalis, Bankia campanellata and B . indica from tropical
habitats. Recent studies on a brackish water species Nausitora hedleyi
(Figs. 27, 28) exhibiting a restricted breeding habit have shown evidence of an interesting sequence of sexual phases. These are of special
interest since this species is one of the very few tropical molluscs with
a restricted breeding habit owing t o the influence of salinity. Details
regarding the sexual condition in specimens examined are presented in
Table IV.
There is a preponderance of ambisexual males among smaller
individuals (1-50 mm) and as growth continues there is a tendency
towards increase in the percentage of females with hermaphrodites
appearing in the intermediate size group (50-200 mm). This suggests
protandry and a probable change of sex from the initial bisexual male
phase to the female phase. Of the 26 hermaphrodites examined only a
few had gametes of both sexual types in the same follicle. Twenty-five
were changing from the male to the female phase and one in the 250 to
391
ponderance of functional males in young populations. Later a greater
part of the individuals were found to produce eggs, these females having
the ability to revert to the male phase. They also found that the transformation from female to male phase may occur abruptly during the
breeding season as well as during the recuperation period and that
gametes of both types capable of self fertilization may be produced in
the same follicle. Coe (1936) showed the existence of a sequence of
functional male and female phases in Teredo navalis-an initial functional male phase followed by a female phase, this often followed by a
second male phase and sometimes by a second female phase. Some
individuals remained in their first male phase for a long time or even
indefinitely and these he named as true males. Coe (1941) later demonstrated protandry with a strong tendency towards rhythmical change of
functional male and female phases in the larviparous Teredo diegensis
and in the oviparous Bankia setacea. He came to the conclusions that
(1) in Teredo diegensis functional hermaphroditism is common without
any sharp demarcation of the sexual phases ; ( 2 ) in T . navalis functional
hermaphroditism is not unusual, although the gonads are histologically
ambisexual during the change of sexual phases ; (3) in Bankia setacea
functional hermaphroditism occurs occasionally in the primary male
phase but subsequent sexual phases are well defined and there is often
a resting stage between them. Grave (1942) subsequently confirmed
Coe’s data on the recurrent functional sex inversion in Teredo navalis
but objected to his interpretation that Teredo is essentially or principally
a protandric hermaphrodite. More recently Ganapati and Nagabhushanam (1954,1959), and Nair (1956) have shown similar sex changes
in Teredo navalis, Bankia campanellata and B . indica from tropical
habitats. Recent studies on a brackish water species Nausitora hedleyi
(Figs. 27, 28) exhibiting a restricted breeding habit have shown evidence of an interesting sequence of sexual phases. These are of special
interest since this species is one of the very few tropical molluscs with
a restricted breeding habit owing t o the influence of salinity. Details
regarding the sexual condition in specimens examined are presented in
Table IV.
There is a preponderance of ambisexual males among smaller
individuals (1-50 mm) and as growth continues there is a tendency
towards increase in the percentage of females with hermaphrodites
appearing in the intermediate size group (50-200 mm). This suggests
protandry and a probable change of sex from the initial bisexual male
phase to the female phase. Of the 26 hermaphrodites examined only a
few had gametes of both sexual types in the same follicle. Twenty-five
were changing from the male to the female phase and one in the 250 to