SOME ASPECTS O F THE BIOLOGY O F THE CHAETOGNATHS
333
spermatozoa into the seminal receptacles. Also Jagersten saw that a
spermatophore placed on the tail quickly empties itself and that the
sperms migrate towards the receptacles.
It can furthermore be observed in some species that the openings
of the receptacles may modify their shape (van Oye, 1931 ; Jiigersten,
1940; Furnestin, 1960). Again this fact leads one to suppose that the
spermatophores must be attached near the genital papilla; if indeed
the spermatophores are experimentally placed on the genital papilla or
in its immediate neighbourhood, a very quick penetration of the
spermatozoa into the receptacles can be seen. As a consequence, the
peculiar structures observed on the vesicles and on the spermatophores
might be considered in some way to be a sort of copulatory organ,
whose form fits one of the female genital orifices thus making mating
between individuals of different species impossible. I n this case the
differences shown by the mature seminal vesicles in even quite closely
related forms would have value as highly discriminative systematic
characters. Thus, for instance, the various forms of Sagitta serratodentata
which are similar in having the typical serrated inside edge of the
hooks, but differ in their biometrical characters and mainly in the shape
of their seminal vesicles, should be considered as true species, as
authoritative modern authors maintain. The differentiation which had
been established by Tokioka (1939a, 1965a), Thomson (1947) and
Furnestin (1953) would find a new and more valid confirmation.
For other genera of chaetognaths the observations on fertilization
are rather fragmentary, certainly far less complete than those concerning the genera Xagitta and Xpadella. David (1958, 1965) has made
some very interesting observations on a specimen of Eukhronia bathyantarctica. Dr. David has been so kind as to send t o nie for examination
this and other specimens. I have thus been able to observe that the
spermatophores are flask-shaped, wrapped externally in an undifferentiated resistant small membrane. There is a prolongation t o this
membrane, the shape of the neck of a bottle or flask, which is slipped
into the female genital orifice, the edges of which protrude remarkably
(Figs. 25 and 26). I n one specimen only was the spermatophore intact ;
in others only the torn membrane was hanging out of the genital
orifices. None of the specimens I examined had mature seminal
vesicles, so that no conclusion could be made as to how the spermatophores form. David, however, believes that they originate from another
individual. Similar observations have also been made by Tchindonova
(1955).
The case of Bathyspadella edentata Tokioka described by Tokioka
(1939b) is also quite interesting. This chaetognath, though very similar
333
spermatozoa into the seminal receptacles. Also Jagersten saw that a
spermatophore placed on the tail quickly empties itself and that the
sperms migrate towards the receptacles.
It can furthermore be observed in some species that the openings
of the receptacles may modify their shape (van Oye, 1931 ; Jiigersten,
1940; Furnestin, 1960). Again this fact leads one to suppose that the
spermatophores must be attached near the genital papilla; if indeed
the spermatophores are experimentally placed on the genital papilla or
in its immediate neighbourhood, a very quick penetration of the
spermatozoa into the receptacles can be seen. As a consequence, the
peculiar structures observed on the vesicles and on the spermatophores
might be considered in some way to be a sort of copulatory organ,
whose form fits one of the female genital orifices thus making mating
between individuals of different species impossible. I n this case the
differences shown by the mature seminal vesicles in even quite closely
related forms would have value as highly discriminative systematic
characters. Thus, for instance, the various forms of Sagitta serratodentata
which are similar in having the typical serrated inside edge of the
hooks, but differ in their biometrical characters and mainly in the shape
of their seminal vesicles, should be considered as true species, as
authoritative modern authors maintain. The differentiation which had
been established by Tokioka (1939a, 1965a), Thomson (1947) and
Furnestin (1953) would find a new and more valid confirmation.
For other genera of chaetognaths the observations on fertilization
are rather fragmentary, certainly far less complete than those concerning the genera Xagitta and Xpadella. David (1958, 1965) has made
some very interesting observations on a specimen of Eukhronia bathyantarctica. Dr. David has been so kind as to send t o nie for examination
this and other specimens. I have thus been able to observe that the
spermatophores are flask-shaped, wrapped externally in an undifferentiated resistant small membrane. There is a prolongation t o this
membrane, the shape of the neck of a bottle or flask, which is slipped
into the female genital orifice, the edges of which protrude remarkably
(Figs. 25 and 26). I n one specimen only was the spermatophore intact ;
in others only the torn membrane was hanging out of the genital
orifices. None of the specimens I examined had mature seminal
vesicles, so that no conclusion could be made as to how the spermatophores form. David, however, believes that they originate from another
individual. Similar observations have also been made by Tchindonova
(1955).
The case of Bathyspadella edentata Tokioka described by Tokioka
(1939b) is also quite interesting. This chaetognath, though very similar