SOME ASPECTS O F T H E BIOLOGY O F T H E CHAETOGNATHS
309
stainable, while those of the epithelium, on the contrary, are strongly
stainable, elongated and closely massed to one another.
There are no substantial differences between the ovaries of E.
bathyantarctica and E. fowleri. The few specimens at my disposal have
not allowed me to obtain transverse sections that may show the
supporting structures of the eggs. I am, therefore, unable to state
whether they are crescent-shaped or not.
I n the male gcnital apparatus there is one peculiarity which should
be mentioned : the particular disposition of the morulac of the germinal
elements in various stages of maturation, which tend to aggregate.
I n conclusion, the fcmale genital apparatus in Xagitta, Spudella,
Pteromgitta and Eukrohnia, although they have the same structural
type, show some remarkable differences. It is interesting to observe
that some species, which live in deep or cold waters, have seminal
pouches with very enlarged ampullae, i.e. Sagitta decipiems, Pterosagitta
draco and Eukrohnia bathyantarctica. I n Xagitta injata as we have seen
both male and female genital apparatus, but especially the male one,
differ considerably from those observed in the other species of Sagitta.
C. Spermatogenesis and oogenesis
1. Xpermatogenesis
Spermatogenesis in chaetognaths has been studied mainly by
Hertwig (1880), Bolles-Lee (1888), Stevens (1903, 1910) and BordAs
(1912, 1914). The subject has been completely neglected since, and
only Tuzet (193 1) has studied spermiohistogenesis and Ghirardelli
(195413) the kariogram of Sagitta inJEata. Spermatogenesis was studied
in the past mainly on S. bipunctata. The most detailed work is that by
BordBs: nevertheless, this worker also missed some details jn the
morphology of the stages of the meiosis. Besides being due to the
techniques employed, this was certainly due to the smallness of the
elements : actually, the chromosomes do not normally exceed a length
of 3 p and in the spermatocytes I1 they are very little over 1 p long.
The authors who have dealt with the subject agree in giving
eighteen as the diploid number. Eighteen chromosomes were found in
8. bipunctata by Boveri (1890), in X. inJlata by Buchner (191Ob) and
Ghirardelli (1954), in X . minima and S. elegans by Stevens (1910). in
S. setosa by Arnaud (1963) and in Xpadella cephaloptera by Ghirardelli
(1959d).
Recently Ghirardelli and Arnaud (1966) have resumed the subject
using the squash technique. They have been able to confirm that apart
from small differences in some details, meiosis in Xagitta setosa occurs
according to the classic scheme. It has been possible to show a
309
stainable, while those of the epithelium, on the contrary, are strongly
stainable, elongated and closely massed to one another.
There are no substantial differences between the ovaries of E.
bathyantarctica and E. fowleri. The few specimens at my disposal have
not allowed me to obtain transverse sections that may show the
supporting structures of the eggs. I am, therefore, unable to state
whether they are crescent-shaped or not.
I n the male gcnital apparatus there is one peculiarity which should
be mentioned : the particular disposition of the morulac of the germinal
elements in various stages of maturation, which tend to aggregate.
I n conclusion, the fcmale genital apparatus in Xagitta, Spudella,
Pteromgitta and Eukrohnia, although they have the same structural
type, show some remarkable differences. It is interesting to observe
that some species, which live in deep or cold waters, have seminal
pouches with very enlarged ampullae, i.e. Sagitta decipiems, Pterosagitta
draco and Eukrohnia bathyantarctica. I n Xagitta injata as we have seen
both male and female genital apparatus, but especially the male one,
differ considerably from those observed in the other species of Sagitta.
C. Spermatogenesis and oogenesis
1. Xpermatogenesis
Spermatogenesis in chaetognaths has been studied mainly by
Hertwig (1880), Bolles-Lee (1888), Stevens (1903, 1910) and BordAs
(1912, 1914). The subject has been completely neglected since, and
only Tuzet (193 1) has studied spermiohistogenesis and Ghirardelli
(195413) the kariogram of Sagitta inJEata. Spermatogenesis was studied
in the past mainly on S. bipunctata. The most detailed work is that by
BordBs: nevertheless, this worker also missed some details jn the
morphology of the stages of the meiosis. Besides being due to the
techniques employed, this was certainly due to the smallness of the
elements : actually, the chromosomes do not normally exceed a length
of 3 p and in the spermatocytes I1 they are very little over 1 p long.
The authors who have dealt with the subject agree in giving
eighteen as the diploid number. Eighteen chromosomes were found in
8. bipunctata by Boveri (1890), in X. inJlata by Buchner (191Ob) and
Ghirardelli (1954), in X . minima and S. elegans by Stevens (1910). in
S. setosa by Arnaud (1963) and in Xpadella cephaloptera by Ghirardelli
(1959d).
Recently Ghirardelli and Arnaud (1966) have resumed the subject
using the squash technique. They have been able to confirm that apart
from small differences in some details, meiosis in Xagitta setosa occurs
according to the classic scheme. It has been possible to show a