308
ELVEZIO GHIRARDELLI
laid are somewhat less, about 100-150 p. It cannot be excluded, therefore, that before or after being laid the eggs may enlarge owing to
imbibition. It is, however, also possible that the large oocytes do not
all ripen at the same time.
I n that case, the high number of eggs contained in each ootheca
could also perhaps justify Sanzo’s supposition, i.e. that the ootheca were
produced by more than one individual. This fact, however, would be
quite remarkable, since P. draco is a rather uncommon species, in the
Mediterranean at least ; it is usually caught singly, a t any rate a t Naples
and Villefranche. The gelatine that wraps the eggs is obviously produced by the glands described above and it has the purpose of protecting the eggs, whose development is the same a s that known for the
other chaetognaths. The increase in the weight of the gclatine causes
the ootheca to sink slowly, protecting the eggs from the effect of the
movements of the waves and of the sudden changes in temperature and
salinity that may occur in the superficial layers.
5. T h e female reproductive apparatus in Eukrohnia
I owe to the great courtesy of Dr. P. M. David the opportunity of
studying some specimens of Eukrohnia bathyantarctica David and of
Eukrohnia Lfotc-leri Ritter-Zahony. In mature specimens, in frontal
sections, the disposition of the parts which constitute the female genital
apparatus is quite similar to that seen in Pterosagitta draco.
There are indeed also in this species two very large seminal
ampullae ; one in each seminal pouch. The seminal pouch originates
from a vagina constituted by the usual two layers of cells; the epithelium shows cubic cells in correspondence to the vagina and tall cells
i n the other regions of the pouch. The latter has no uniform calibre :
along its course it has one or two widenings full of spermatozoa. At
its cephalic end there is a large ampulla about 1 mm long ; the whole
length of the pouch plus ampulla may nieasure 2-3 mm. JThen these
ampullae are completely full of spermatozoa in their central region
they may show masses of sperms more aggregated than in the peripheral portion. The lining of the seminal receptacle seems to consist
at some points of only one layer of cells: this, however, may be
accounted for in Eukrohnia as in Pterosagitta through the stretching to
which the walls of the pouch are subject.
The mature eggs near the time of laying are few and large, and their
cytoplasm is full of grains of yolk. The younger eggs show, on t h e
contrary, the same features as those known in other chaetognaths and
they are inserted on the ovarian epithelium by means of the usual
peduncle made of two cells: the nuclei of the latter are only slightly
ELVEZIO GHIRARDELLI
laid are somewhat less, about 100-150 p. It cannot be excluded, therefore, that before or after being laid the eggs may enlarge owing to
imbibition. It is, however, also possible that the large oocytes do not
all ripen at the same time.
I n that case, the high number of eggs contained in each ootheca
could also perhaps justify Sanzo’s supposition, i.e. that the ootheca were
produced by more than one individual. This fact, however, would be
quite remarkable, since P. draco is a rather uncommon species, in the
Mediterranean at least ; it is usually caught singly, a t any rate a t Naples
and Villefranche. The gelatine that wraps the eggs is obviously produced by the glands described above and it has the purpose of protecting the eggs, whose development is the same a s that known for the
other chaetognaths. The increase in the weight of the gclatine causes
the ootheca to sink slowly, protecting the eggs from the effect of the
movements of the waves and of the sudden changes in temperature and
salinity that may occur in the superficial layers.
5. T h e female reproductive apparatus in Eukrohnia
I owe to the great courtesy of Dr. P. M. David the opportunity of
studying some specimens of Eukrohnia bathyantarctica David and of
Eukrohnia Lfotc-leri Ritter-Zahony. In mature specimens, in frontal
sections, the disposition of the parts which constitute the female genital
apparatus is quite similar to that seen in Pterosagitta draco.
There are indeed also in this species two very large seminal
ampullae ; one in each seminal pouch. The seminal pouch originates
from a vagina constituted by the usual two layers of cells; the epithelium shows cubic cells in correspondence to the vagina and tall cells
i n the other regions of the pouch. The latter has no uniform calibre :
along its course it has one or two widenings full of spermatozoa. At
its cephalic end there is a large ampulla about 1 mm long ; the whole
length of the pouch plus ampulla may nieasure 2-3 mm. JThen these
ampullae are completely full of spermatozoa in their central region
they may show masses of sperms more aggregated than in the peripheral portion. The lining of the seminal receptacle seems to consist
at some points of only one layer of cells: this, however, may be
accounted for in Eukrohnia as in Pterosagitta through the stretching to
which the walls of the pouch are subject.
The mature eggs near the time of laying are few and large, and their
cytoplasm is full of grains of yolk. The younger eggs show, on t h e
contrary, the same features as those known in other chaetognaths and
they are inserted on the ovarian epithelium by means of the usual
peduncle made of two cells: the nuclei of the latter are only slightly