200
ELVEZIO GHIRARDELLI
just in front of the septum that divides the trunk region from the tail.
The male reproductive apparatus completely occupies the coelom of the
caudal segment, except in Xaqitta inflata, and is separated from the
trunk by a transverse septum (Fig. 1). It is formed by the testes, vas
deferens and seminal vesicles, paired structures symmetrically disposed along a longitudinal septum that divides the caudal coelom in
half. This septum is composed of a homogeneous median plate (lamina),
covered on both faces by a cubic epithelium which is probably ciliated
(Burfield, 1927). The anterior ventral part of the septum divides t o
form a triangular space in which the anal orifice is situated.
In the upper part the longitudinal septum is connected to the
transverse septum ; the two chambers into which the coelom is divided,
and which look more or less like pyramids, are further divided into
two by two secondary longitudinal septa. These latter are extremely
thin and do not show any peculiar structure except in the ventral and
dorsal lines where some nuclei can be seen. Each of these septa is
attached on the anterior side t o the inner wall of the body, a little
behind the caudal septum. On the back, the secondary septum ends
a t the level of the seminal vesicles. I n this way the subdivision of each
half of the coelom cavity is not complete and both in the anterior and
in the posterior part the materials contained in the coelom can circulate
freely (Fig. 1). Each of the two chambers into which the coelom is
divided is partially occupied by a testis: a more or less solid body,
rather flattened, situated in the anterior part of the chamber, attached
to the wall in the region of the lateral area and ventral longitudinal
muscle. I n side view, the testis appears as a thin band extending from
the transverse septum to about one-half of the tail length. Each testis
is covered by a thin endothelial layer. From the testes, groups of
spermatogonia continuously depart and they continue their development while floating in the liquid which fills the coelomic cavity.
Masses of elements all in the same stage of development (polyplasts
of Bolles-Lee or sperm morulae) or very nearly in the same stages
(Bordks, 1914; Ghirardelli and Arnaud, 1966) are so formed. According
to Stevens, however, different stages of spermatogenesis can also
co-exist in the same mass. The masses are constantly moving and in
each of the two chambers in which the caudal coelom is divided, they
move in the following manner: from the posterior end of the coelom
they move up along the external wall until they reach the caudal
septum ; they then pass through the opening in the secondary longitudinal septum and move towards the tail passing between the
secondary and the median septa. Their movement is more or less rapid
depending on the species and the degree of fullness of the coelom. In
ELVEZIO GHIRARDELLI
just in front of the septum that divides the trunk region from the tail.
The male reproductive apparatus completely occupies the coelom of the
caudal segment, except in Xaqitta inflata, and is separated from the
trunk by a transverse septum (Fig. 1). It is formed by the testes, vas
deferens and seminal vesicles, paired structures symmetrically disposed along a longitudinal septum that divides the caudal coelom in
half. This septum is composed of a homogeneous median plate (lamina),
covered on both faces by a cubic epithelium which is probably ciliated
(Burfield, 1927). The anterior ventral part of the septum divides t o
form a triangular space in which the anal orifice is situated.
In the upper part the longitudinal septum is connected to the
transverse septum ; the two chambers into which the coelom is divided,
and which look more or less like pyramids, are further divided into
two by two secondary longitudinal septa. These latter are extremely
thin and do not show any peculiar structure except in the ventral and
dorsal lines where some nuclei can be seen. Each of these septa is
attached on the anterior side t o the inner wall of the body, a little
behind the caudal septum. On the back, the secondary septum ends
a t the level of the seminal vesicles. I n this way the subdivision of each
half of the coelom cavity is not complete and both in the anterior and
in the posterior part the materials contained in the coelom can circulate
freely (Fig. 1). Each of the two chambers into which the coelom is
divided is partially occupied by a testis: a more or less solid body,
rather flattened, situated in the anterior part of the chamber, attached
to the wall in the region of the lateral area and ventral longitudinal
muscle. I n side view, the testis appears as a thin band extending from
the transverse septum to about one-half of the tail length. Each testis
is covered by a thin endothelial layer. From the testes, groups of
spermatogonia continuously depart and they continue their development while floating in the liquid which fills the coelomic cavity.
Masses of elements all in the same stage of development (polyplasts
of Bolles-Lee or sperm morulae) or very nearly in the same stages
(Bordks, 1914; Ghirardelli and Arnaud, 1966) are so formed. According
to Stevens, however, different stages of spermatogenesis can also
co-exist in the same mass. The masses are constantly moving and in
each of the two chambers in which the caudal coelom is divided, they
move in the following manner: from the posterior end of the coelom
they move up along the external wall until they reach the caudal
septum ; they then pass through the opening in the secondary longitudinal septum and move towards the tail passing between the
secondary and the median septa. Their movement is more or less rapid
depending on the species and the degree of fullness of the coelom. In