Ontogeny of Marine Turtle Gonads
205
from the mesonephros, carries only sperm in the adult. As testicular development
continues, the paramesonephric duct begins to degenerate (Raynaud et al., 1970;
Raynaud and Pieau, 1985).
In the female, the paramesonephric (müllerian) ducts develop from coelomic
epithelium that thickens and forms a craniocaudal groove, the edges of which fuse
to form a tube (Raynaud and Pieau, 1985; Wibbels et al., 1999b). The cephalic end
of each tube opens as a funnel-shaped ostium tubae into the coelomic cavity. The
ostium tubae becomes the infundibulum in the mature oviduct. The caudal end of
the paramesonephric duct extends into the retroperitoneal connective tissue; as it
develops, it parallels the mesonephric duct and eventually forms a connection with
the cloaca (Raynaud and Pieau, 1985). In C. mydas , oviducts are indicated by stage
23 (13 mm body length), and the anterior end is formed by stage 25 (21 mm,
Weidersheim, 1890b; Wilson, 1900).
Paramesonephric ducts develop in both sexes but function as oviducts only in
females. Remnants may be retained in functional males. For example, in loggerhead
turtles and less frequently in green turtles examined via necropsy and laparoscopy,
the paramesonephric duct may persist and remain visible adjacent to the testis but
terminate within the mesentery posteriorly and not connect to the cloaca (Limpus
et al., 1982). The less degenerated paramesonephric ducts in males structurally
resemble the female oviduct except that the lumen is lined with a squamous rather
than a columnar epithelium. The function of the persistent paramesonephric duct in
adult males is unresolved.
The cloaca is a “common sewer” that receives the output of the urogenital
ducts and intestinal waste and passes to the exterior of the body. The cloaca
originates from a diverticulum of the hindgut, fusing with the inward pocketing
proctodeum (Raynaud and Pieau, 1985). The result is a tube that is separated from
the intestine by a sphincter and has openings from the oviducts (female) or vas
deferens (male), contains the penis or clitoris, and receives fluid from the bladder
(derived from the allantois).
During development, the urinogenital prominence is first visible in stage 18
(Miller, 1985); by stage 23, the bulge extends to about the posterior edge of the
hind digital plate. The undifferentiated urinogenital papilla is not visible until
stage 24; the papilla is withdrawn by stage 28. In the female, it forms the clitoris;
it is assumed, by homology, to follow the same pattern of differentiation as the
penis, albeit on a smaller scale, although there are no direct studies. The penis is
attached anteriorly on the floor of the male cloaca. It is formed from a pair of
longitudinal vascular, spongy ridges of tissue (corpora cavernosa) that converge
distally to form the glans penis with a medial groove (seminal furrow) (Raynaud
and Pieau, 1985). The erected, adult penis results from the corpora cavernosa
being engorged with blood to seal the medial seminal furrow into a tube (Figure
7.1). The engorgement of the corpora cavernosa extends the penis from the cloaca
during copulation. No observations have been published that indicate whether the
penis erects as it is inserted into the female or before. However, during our
numerous courtship observations of males mounted on females, none have been
observed with an erect penis outside the female.
1123 book.book Page 205 Monday, November 11, 2002 11:11 AM
205
from the mesonephros, carries only sperm in the adult. As testicular development
continues, the paramesonephric duct begins to degenerate (Raynaud et al., 1970;
Raynaud and Pieau, 1985).
In the female, the paramesonephric (müllerian) ducts develop from coelomic
epithelium that thickens and forms a craniocaudal groove, the edges of which fuse
to form a tube (Raynaud and Pieau, 1985; Wibbels et al., 1999b). The cephalic end
of each tube opens as a funnel-shaped ostium tubae into the coelomic cavity. The
ostium tubae becomes the infundibulum in the mature oviduct. The caudal end of
the paramesonephric duct extends into the retroperitoneal connective tissue; as it
develops, it parallels the mesonephric duct and eventually forms a connection with
the cloaca (Raynaud and Pieau, 1985). In C. mydas , oviducts are indicated by stage
23 (13 mm body length), and the anterior end is formed by stage 25 (21 mm,
Weidersheim, 1890b; Wilson, 1900).
Paramesonephric ducts develop in both sexes but function as oviducts only in
females. Remnants may be retained in functional males. For example, in loggerhead
turtles and less frequently in green turtles examined via necropsy and laparoscopy,
the paramesonephric duct may persist and remain visible adjacent to the testis but
terminate within the mesentery posteriorly and not connect to the cloaca (Limpus
et al., 1982). The less degenerated paramesonephric ducts in males structurally
resemble the female oviduct except that the lumen is lined with a squamous rather
than a columnar epithelium. The function of the persistent paramesonephric duct in
adult males is unresolved.
The cloaca is a “common sewer” that receives the output of the urogenital
ducts and intestinal waste and passes to the exterior of the body. The cloaca
originates from a diverticulum of the hindgut, fusing with the inward pocketing
proctodeum (Raynaud and Pieau, 1985). The result is a tube that is separated from
the intestine by a sphincter and has openings from the oviducts (female) or vas
deferens (male), contains the penis or clitoris, and receives fluid from the bladder
(derived from the allantois).
During development, the urinogenital prominence is first visible in stage 18
(Miller, 1985); by stage 23, the bulge extends to about the posterior edge of the
hind digital plate. The undifferentiated urinogenital papilla is not visible until
stage 24; the papilla is withdrawn by stage 28. In the female, it forms the clitoris;
it is assumed, by homology, to follow the same pattern of differentiation as the
penis, albeit on a smaller scale, although there are no direct studies. The penis is
attached anteriorly on the floor of the male cloaca. It is formed from a pair of
longitudinal vascular, spongy ridges of tissue (corpora cavernosa) that converge
distally to form the glans penis with a medial groove (seminal furrow) (Raynaud
and Pieau, 1985). The erected, adult penis results from the corpora cavernosa
being engorged with blood to seal the medial seminal furrow into a tube (Figure
7.1). The engorgement of the corpora cavernosa extends the penis from the cloaca
during copulation. No observations have been published that indicate whether the
penis erects as it is inserted into the female or before. However, during our
numerous courtship observations of males mounted on females, none have been
observed with an erect penis outside the female.
1123 book.book Page 205 Monday, November 11, 2002 11:11 AM