330
ELVEZIO CHIRARDELLI
a part in this process by helping t o keep the migrating spermatozoa
moving in the right direction.
On fixed specimens of Xagitta ferox Doncaster from the seas around
Madagascar, Dallot (personal communication) has often observed on
the ventral face of the anterior fins a voluminous spermatophore
attached by means of its adhesive sucker. More than one spermatophore, up to three, can sometimes be seen on a single specimen, and
the seminal vesicles of the same animal may be either full or empty.
Even in Sagitta neglecta Aida and X . bedoti BBranek, Dallot has seen
spermatophores, but they were placed indifferently on this or that
point of the body.
According to Gray (1930) the spermatozoa might exceptionally
enter the seminal receptacles by going through the caudal septum.
Accurate observations in the laboratory, on the fertilization of the
genus Xagitta have been made by Jagersten (1940), Dallot (1966) and
Murakami (1959) who has been able to rear S. crassa for 3 months.
Jagersten, who studied S. setosn, gave an accurate description of the
fertilization process. As we have already said, this writer thinks that
in Sagitta there is usually self-fertilization only and no mutual mating.
The breakage of the seminal vesicles occurs along pre-ordained lines
which Jagersten described. The spermatozoa migrate along the tail
towards the caudal septum. The modes of the migration itself may
differ in different specimens. The process occurs mostly in the night
hours. Jagersten also kept specimens isolated one from another, and
observed that if their seminal receptacles had been empty in the
evening, in the morning they were full while one or both seminal
vesicles had emptied. The migration from one vesicle is not necessarily
always directly towards the seminal receptacle on the same side ; the
sperms may actually migrate to the opposite side also and this migration is not prevented by the sudden movements of the animal, though
obviously a certain quantity of spermatozoa may get lost. A further
proof of the necessity of self-fertilization is, according t o Jagersten,
the fact that young individuals whose seminal vesicles have never been
filled, never show sperms in their seminal receptacles. Furthermore,
specimens with full seminal receptacles always have empty scminsl
vesicles and vice versa.
Some objections can, however, be raised against Jagersten’s conclusions. The chaetognaths are indeed protandric hermaphrodite
organisms in which the testes mature sooner than the ovaries. It is
apparent that if an individual has never had full seminal vesicles, it
is not yet completely mature at the male sex, and still less at its female
sex : it is then unlikely or a t least difficult for fertilization t o occur. The
ELVEZIO CHIRARDELLI
a part in this process by helping t o keep the migrating spermatozoa
moving in the right direction.
On fixed specimens of Xagitta ferox Doncaster from the seas around
Madagascar, Dallot (personal communication) has often observed on
the ventral face of the anterior fins a voluminous spermatophore
attached by means of its adhesive sucker. More than one spermatophore, up to three, can sometimes be seen on a single specimen, and
the seminal vesicles of the same animal may be either full or empty.
Even in Sagitta neglecta Aida and X . bedoti BBranek, Dallot has seen
spermatophores, but they were placed indifferently on this or that
point of the body.
According to Gray (1930) the spermatozoa might exceptionally
enter the seminal receptacles by going through the caudal septum.
Accurate observations in the laboratory, on the fertilization of the
genus Xagitta have been made by Jagersten (1940), Dallot (1966) and
Murakami (1959) who has been able to rear S. crassa for 3 months.
Jagersten, who studied S. setosn, gave an accurate description of the
fertilization process. As we have already said, this writer thinks that
in Sagitta there is usually self-fertilization only and no mutual mating.
The breakage of the seminal vesicles occurs along pre-ordained lines
which Jagersten described. The spermatozoa migrate along the tail
towards the caudal septum. The modes of the migration itself may
differ in different specimens. The process occurs mostly in the night
hours. Jagersten also kept specimens isolated one from another, and
observed that if their seminal receptacles had been empty in the
evening, in the morning they were full while one or both seminal
vesicles had emptied. The migration from one vesicle is not necessarily
always directly towards the seminal receptacle on the same side ; the
sperms may actually migrate to the opposite side also and this migration is not prevented by the sudden movements of the animal, though
obviously a certain quantity of spermatozoa may get lost. A further
proof of the necessity of self-fertilization is, according t o Jagersten,
the fact that young individuals whose seminal vesicles have never been
filled, never show sperms in their seminal receptacles. Furthermore,
specimens with full seminal receptacles always have empty scminsl
vesicles and vice versa.
Some objections can, however, be raised against Jagersten’s conclusions. The chaetognaths are indeed protandric hermaphrodite
organisms in which the testes mature sooner than the ovaries. It is
apparent that if an individual has never had full seminal vesicles, it
is not yet completely mature at the male sex, and still less at its female
sex : it is then unlikely or a t least difficult for fertilization t o occur. The