SOME ASPECTS OF THE BIOLOGY OF THE CIIAETOGNATHS
297
Xagitta lyra, for instance, the fore end has the form of the bull) of the
thermometer (Grassi, 1883). The same occurs in 8. inJlata, while in 8.
bipunctata the seminal pouch shows irregular thickenings along its
whole extension. I n Xagitta decipiens Fowler it is club-shaped. Also
the supporting formation shows some difference, in S. inJtata for
instance, it is only approximately crescent-shaped. The epithelial cells
around the lumen of the pouch do not show two layers as in other
species of Xagitta but are placed like rays around the lumen of the
seminal pouch. Dorsally and ventrally to the pouch, the cells display
their maximum length. They are club-like cells with the more enlarged
end orientated towards the median region of the body ; the nucleus is
also placed towards this end (Fig. 9). I n the median region of the
pouch, the cells are instead lower though still presenting the clubshaped form. I n X. bipunctata in the median region of the crescent the
epithelium from being cylindrical becomes cubic and this is particularly
apparent in the illustrations (Fig. 9).
On the external side of the pouch, i.e. on the side toward the body
wall, both in S. bipunctata and in S. inJlata the syncytium is lined with
rather flat cells.
2. The accessory fertilization cells
I n order to complete the description of the reproductive apparatus
in Xagitta, mention must be made of the so-called accessory fertilization
cells.
These have been called by different names: “ picciuolo ” (stem) by
Grassi (1883) in Xagitta and Spadella, “ Aufhangenapparat ” (Buchner
1910a), “ Strangzellen” (Buchner, 1910b) in Xagitta, “accessory fertilization cells” (Stevens, 1910) inXagitta, “Zweizellenapparat ” (Elpatiewsky,
1913) in Xagitta, “ appareil pluricellulaire ”, “ appareil de suspension ”
(Vasiljev, 1925) inSpadella, “ aparato micropilar ”, “ celulas sospensoras ”
(BordBs, 1920) in Sagitta. Some of these terms give a clear idea of the
purpose of these cells, which is to connect the eggs to the seminal pouch
ensuring at the same time the passage of the spermatozoon from the
scminal pouch to the egg. The suspension apparatus is one of the most
peculiar structures in Chaetognatha, which are themselves peculiar
organisms.
As we have already seen, Grassi believed the suspension apparatus
to be made of one cell only in Xagitta while being multicellular in
Xpadelln. Buchner and Stevens have accurately described the suspension
apparatus in Xagitta and Vasiljev has done so in Xpndella. I n Sagitta
bipunctata and in Xpadelln cephaloptera I have been able to confirm that
the suspension apparatus consists of two cells of which the lower one is
297
Xagitta lyra, for instance, the fore end has the form of the bull) of the
thermometer (Grassi, 1883). The same occurs in 8. inJlata, while in 8.
bipunctata the seminal pouch shows irregular thickenings along its
whole extension. I n Xagitta decipiens Fowler it is club-shaped. Also
the supporting formation shows some difference, in S. inJtata for
instance, it is only approximately crescent-shaped. The epithelial cells
around the lumen of the pouch do not show two layers as in other
species of Xagitta but are placed like rays around the lumen of the
seminal pouch. Dorsally and ventrally to the pouch, the cells display
their maximum length. They are club-like cells with the more enlarged
end orientated towards the median region of the body ; the nucleus is
also placed towards this end (Fig. 9). I n the median region of the
pouch, the cells are instead lower though still presenting the clubshaped form. I n X. bipunctata in the median region of the crescent the
epithelium from being cylindrical becomes cubic and this is particularly
apparent in the illustrations (Fig. 9).
On the external side of the pouch, i.e. on the side toward the body
wall, both in S. bipunctata and in S. inJlata the syncytium is lined with
rather flat cells.
2. The accessory fertilization cells
I n order to complete the description of the reproductive apparatus
in Xagitta, mention must be made of the so-called accessory fertilization
cells.
These have been called by different names: “ picciuolo ” (stem) by
Grassi (1883) in Xagitta and Spadella, “ Aufhangenapparat ” (Buchner
1910a), “ Strangzellen” (Buchner, 1910b) in Xagitta, “accessory fertilization cells” (Stevens, 1910) inXagitta, “Zweizellenapparat ” (Elpatiewsky,
1913) in Xagitta, “ appareil pluricellulaire ”, “ appareil de suspension ”
(Vasiljev, 1925) inSpadella, “ aparato micropilar ”, “ celulas sospensoras ”
(BordBs, 1920) in Sagitta. Some of these terms give a clear idea of the
purpose of these cells, which is to connect the eggs to the seminal pouch
ensuring at the same time the passage of the spermatozoon from the
scminal pouch to the egg. The suspension apparatus is one of the most
peculiar structures in Chaetognatha, which are themselves peculiar
organisms.
As we have already seen, Grassi believed the suspension apparatus
to be made of one cell only in Xagitta while being multicellular in
Xpadelln. Buchner and Stevens have accurately described the suspension
apparatus in Xagitta and Vasiljev has done so in Xpndella. I n Sagitta
bipunctata and in Xpadelln cephaloptera I have been able to confirm that
the suspension apparatus consists of two cells of which the lower one is