SOME ASPECTS OF THE BIOLOGY O F THE CHAETOGNATHS
331
second objection is that in other species and in S. setosa from other
localities (Gulf of Naples, Gulf of Trieste, Villefranche) it is not infrequent to find specimens which have a t the same time full seminal
vesicles and receptacles. Jagersten finally does not exclude that in the
course of phylogeny reciprocal fertilization may have been substituted
by self-fertilization. The evidence of reciprocal fertilization is in a
cup-shaped structure that is to be found on the seminal vesicles; it
detaches itself, together with the contents of the vesicles, forming a
spermatophore which seems to be provided with an organ-the cup
itself-so made as to adhere to the body of another individual. We shall
have the opportunity of dealing again with this and other similar
formations which are to be found in other species of Sagitta (p. 332).
Dallot (1966) also believes that fertilization is not reciprocal. He
was able to raise specimens of S. setosa in isolation and found that in
spite of this about 50% of the spawning gave fertilized eggs. He also
observcd that the same animal might lay successively unfertilized eggs
and then fertilized ones, or also that the contrary might happen; all
the eggs of one spawning are, however, in the same state.
There were also specimens that always laid fertilized eggs and others
only unfertilized eggs. According to Dallot, the greater number of
unfertilized eggs could be explained by a state of immaturity of the
seminal vesicles, or by the fact that though mature they do not open.
He says that the sterility of a spawning can be guessed in advance if a
short time before the expulsion of the eggs one sees the seminal vesicles
full of sperms. On the other hand, seminal vesicles which open before
laying provide a good indication of fertilization. Dallot has been able
to confirm what Jagersten had already seen, namely, that the filling
of the seminal vesicles takes place periodically. After the wall in the
mature vesicles breaks, a new spermatophore forms which will be freed
a little while later. Dallot has also seen that this cycle supersedes that
of the ovary : the formation of a spermatophore is generally concurrent
with the period of growth of the ovary following a deposition. Finally,
he was able to observe that generally the number of the cycles in the
male reproductive organ is the same as that of the female apparatus.
The periodicity of ripening both of the ovary and vesiculae seminales is
2 1 h. It also seems that the synchronous activity of the seminal vesicles
and of the ovaries is an essential factor to ensure the success of selffertilization. The laying of the eggs occurs before dawn. Dallot has
further seen that in the animals gathered and placed under breeding
conditions before their ovaries were completely mature, the seminal
receptacles regularly appear empty. He thus excludes the possibility
that fertilized eggs laid by animals just placed under breeding
331
second objection is that in other species and in S. setosa from other
localities (Gulf of Naples, Gulf of Trieste, Villefranche) it is not infrequent to find specimens which have a t the same time full seminal
vesicles and receptacles. Jagersten finally does not exclude that in the
course of phylogeny reciprocal fertilization may have been substituted
by self-fertilization. The evidence of reciprocal fertilization is in a
cup-shaped structure that is to be found on the seminal vesicles; it
detaches itself, together with the contents of the vesicles, forming a
spermatophore which seems to be provided with an organ-the cup
itself-so made as to adhere to the body of another individual. We shall
have the opportunity of dealing again with this and other similar
formations which are to be found in other species of Sagitta (p. 332).
Dallot (1966) also believes that fertilization is not reciprocal. He
was able to raise specimens of S. setosa in isolation and found that in
spite of this about 50% of the spawning gave fertilized eggs. He also
observcd that the same animal might lay successively unfertilized eggs
and then fertilized ones, or also that the contrary might happen; all
the eggs of one spawning are, however, in the same state.
There were also specimens that always laid fertilized eggs and others
only unfertilized eggs. According to Dallot, the greater number of
unfertilized eggs could be explained by a state of immaturity of the
seminal vesicles, or by the fact that though mature they do not open.
He says that the sterility of a spawning can be guessed in advance if a
short time before the expulsion of the eggs one sees the seminal vesicles
full of sperms. On the other hand, seminal vesicles which open before
laying provide a good indication of fertilization. Dallot has been able
to confirm what Jagersten had already seen, namely, that the filling
of the seminal vesicles takes place periodically. After the wall in the
mature vesicles breaks, a new spermatophore forms which will be freed
a little while later. Dallot has also seen that this cycle supersedes that
of the ovary : the formation of a spermatophore is generally concurrent
with the period of growth of the ovary following a deposition. Finally,
he was able to observe that generally the number of the cycles in the
male reproductive organ is the same as that of the female apparatus.
The periodicity of ripening both of the ovary and vesiculae seminales is
2 1 h. It also seems that the synchronous activity of the seminal vesicles
and of the ovaries is an essential factor to ensure the success of selffertilization. The laying of the eggs occurs before dawn. Dallot has
further seen that in the animals gathered and placed under breeding
conditions before their ovaries were completely mature, the seminal
receptacles regularly appear empty. He thus excludes the possibility
that fertilized eggs laid by animals just placed under breeding