SOME ASPECTS O F T H E BIOLOGY O F T H E CHAETOGNATHS
307
are numerous glandular elements which are filled-at the extremities
turned towards the lumen of the tubule-with grains of a secretion
which is strongly eosinophilic. Glandular cells are also present on the
inner wallof the seminal pouch, so that often among the eggs nearer tothe
pouch it is possible to observe grains of a secretion quite similar to the
ones just mentioned. The vagina opens at the end of a very apparent
papilla, whose walls are formed externally by a cylindrical epithelium
which is cleanly separated by a basement membrane from another layer
of flat elongated cells which are in turn separated from an innermost
layer made of glandular cells only, rich in secretion.
The oocytes in Pterosagitta have a somewhat different distribution
from the one found in other chaetognaths. I n the region of the vagina
the epithelium of the seminal pouch inflects towards the median line
forming a sort of cap in which some oocytes are found. These show
differences according to their stage of maturity : the younger ones have a
large strongly stainable nucleus, with homogeneous cytoplasm, and are
regularly intercalated with oocytes in their last stage of growth, whose
cytoplasm is filled with yolk. The oocytes nearer to the wall come in
contact with the seminal pouch by means of a formation which is
similar to the one observed in Spadella and Xagitta. The fertilization
apparatus on the whole seems, however, a little more elongated. Also
in Pterosagitta, near the principal cells which constitute the fertilization
apparatus, others can be observed whose purpose is not always very
clear: they serve probably as a support to the accessory fertilization
cells.
I n frontal sections the ovary shows up to two layers of oocytes in
their last stage of growth ; the second layer can come in contact with
the walls of the seminal pouch because these eggs have a pear-like
shape and a peduncle long enough to penetrate among the oocytes of
the inner layer and reach the supporting epithelium. It is, however,
probable that these eggs, as soon as they are fertilized, lose their contact
with the epithelium.
The eggs in each ovary are quite numerous : one may count 100-150
in their last stages of growth. This very large number of eggs may
explain the observation made by Sanzo (1937) in the Straits of Messina.
This worker found some pelagic ootheca of Pterosagitta draco : each of
these ootheca were from 5 to 8 mm in length and from 5 to 6 mm in
breadth and contained from 200 to 300 eggs. Considering that the eggs
had a diameter of about 300 p, and comparing them with the measurements of the adult animal, Sanzo believed it was rather unlikely that
such a number of eggs could have been laid by one individual. I n my
preparations I have found that the dimensions of the eggs ready to be
307
are numerous glandular elements which are filled-at the extremities
turned towards the lumen of the tubule-with grains of a secretion
which is strongly eosinophilic. Glandular cells are also present on the
inner wallof the seminal pouch, so that often among the eggs nearer tothe
pouch it is possible to observe grains of a secretion quite similar to the
ones just mentioned. The vagina opens at the end of a very apparent
papilla, whose walls are formed externally by a cylindrical epithelium
which is cleanly separated by a basement membrane from another layer
of flat elongated cells which are in turn separated from an innermost
layer made of glandular cells only, rich in secretion.
The oocytes in Pterosagitta have a somewhat different distribution
from the one found in other chaetognaths. I n the region of the vagina
the epithelium of the seminal pouch inflects towards the median line
forming a sort of cap in which some oocytes are found. These show
differences according to their stage of maturity : the younger ones have a
large strongly stainable nucleus, with homogeneous cytoplasm, and are
regularly intercalated with oocytes in their last stage of growth, whose
cytoplasm is filled with yolk. The oocytes nearer to the wall come in
contact with the seminal pouch by means of a formation which is
similar to the one observed in Spadella and Xagitta. The fertilization
apparatus on the whole seems, however, a little more elongated. Also
in Pterosagitta, near the principal cells which constitute the fertilization
apparatus, others can be observed whose purpose is not always very
clear: they serve probably as a support to the accessory fertilization
cells.
I n frontal sections the ovary shows up to two layers of oocytes in
their last stage of growth ; the second layer can come in contact with
the walls of the seminal pouch because these eggs have a pear-like
shape and a peduncle long enough to penetrate among the oocytes of
the inner layer and reach the supporting epithelium. It is, however,
probable that these eggs, as soon as they are fertilized, lose their contact
with the epithelium.
The eggs in each ovary are quite numerous : one may count 100-150
in their last stages of growth. This very large number of eggs may
explain the observation made by Sanzo (1937) in the Straits of Messina.
This worker found some pelagic ootheca of Pterosagitta draco : each of
these ootheca were from 5 to 8 mm in length and from 5 to 6 mm in
breadth and contained from 200 to 300 eggs. Considering that the eggs
had a diameter of about 300 p, and comparing them with the measurements of the adult animal, Sanzo believed it was rather unlikely that
such a number of eggs could have been laid by one individual. I n my
preparations I have found that the dimensions of the eggs ready to be