200
The Biology of Sea Turtles, Vol. II
context of what was known about amphibians, birds, and mammals (Wiedersheim,
1890a; 1890b; Wilson, 1896; 1900; Allen, 1906; Risley, 1933). Studies on the
development of the cloaca and copulatory organs in turtles (Mitsukuri, 1896; Fleishmann and Hellmuth, 1902 in Fleishmann, 1902) and of the peritoneal canals (Moens,
1912) have contributed to the understanding of the morphology of the genital
structures. Over the years, many specific aspects related to urinogenital development
(i.e., germ cell movement, Jordan, 1917; kidney development, Burland, 1912; wolffian duct, Mitsukuri, 1888) have been examined; most of this work was descriptive
and, in its day, theoretical. In 1977, Fox (1977) reviewed the ontogeny of the
urinogenital system of reptiles. He traced the history of the kidney and associated
ducts while comparing the descriptive morphology and conclusions drawn from the
older studies dealing with the pronephros, mesonephros, and metanephros; he also
dealt with the development of the gonads and associated ducts. More recently, the
origin and development of oocytes (Hubert, 1985) and the embryonic development
of the genital system in reptiles (Raynaud and Pieau, 1985) have been reexamined,
with the emphasis on lizards and comments on turtles. At the same time, Ewert
(1985) reviewed general embryology of turtles, and Miller (1985) described a series
of developmental stages for marine turtles with emphasis on the Cheloniidae.
Detailed descriptions of the development of Dermochelys coriacea were presented
by Renous et al. (1989).
Although studies on marine turtles have contributed to the understanding of the
development of the genital system in reptiles, no review has specifically addressed
the ontogeny of marine turtle gonads. This chapter traces the ontogeny (morphology)
of the gonads and associated ducts of marine turtles from embryogenesis through
puberty to the adult, including changes linked with the reproductive cycle; lesser
emphasis is placed on the development of the copulatory organs. The primary
information is derived from studies on marine turtles; secondary support is obtained
from studies on other turtles and, in turn, other reptiles. The approach focuses on
marine turtles as much as possible rather than addressing the topic of gonadal
ontogeny of reptiles (see Fox, 1977; Raynaud and Pieau, 1985). It should be remembered that morphological change, whether it be associated with development, growth,
maturation, or reproduction, should not be viewed in isolation; the ontogenetic
changes are driven by a complex suite of genetically coded interactive endocrine
changes that occur in the context of endogenous and exogenous events throughout
the life of the turtle (Owens, 1997).
7.2 EMBRYOGENESIS
During ovulation, multiple unfertilized ova are expelled from the ovary into the body
cavity, from which they pass into the infundibulum of the oviduct; multiple ovulations for the entire clutch occur over a short time interval (Aitken et al., 1976; Owens,
1980). Fertilization occurs in the anterior of the oviduct (infundibulum or aglandular
zone) before each ovum is surrounded by albumen (Miller, 1985). Cleavage and the
formation of the gastrula occur as each ovum passes down the oviduct (Miller, 1985).
Sequentially during this passage, each ovum is surrounded by albumen, the shell
1123 book.book Page 200 Monday, November 11, 2002 11:11 AM
The Biology of Sea Turtles, Vol. II
context of what was known about amphibians, birds, and mammals (Wiedersheim,
1890a; 1890b; Wilson, 1896; 1900; Allen, 1906; Risley, 1933). Studies on the
development of the cloaca and copulatory organs in turtles (Mitsukuri, 1896; Fleishmann and Hellmuth, 1902 in Fleishmann, 1902) and of the peritoneal canals (Moens,
1912) have contributed to the understanding of the morphology of the genital
structures. Over the years, many specific aspects related to urinogenital development
(i.e., germ cell movement, Jordan, 1917; kidney development, Burland, 1912; wolffian duct, Mitsukuri, 1888) have been examined; most of this work was descriptive
and, in its day, theoretical. In 1977, Fox (1977) reviewed the ontogeny of the
urinogenital system of reptiles. He traced the history of the kidney and associated
ducts while comparing the descriptive morphology and conclusions drawn from the
older studies dealing with the pronephros, mesonephros, and metanephros; he also
dealt with the development of the gonads and associated ducts. More recently, the
origin and development of oocytes (Hubert, 1985) and the embryonic development
of the genital system in reptiles (Raynaud and Pieau, 1985) have been reexamined,
with the emphasis on lizards and comments on turtles. At the same time, Ewert
(1985) reviewed general embryology of turtles, and Miller (1985) described a series
of developmental stages for marine turtles with emphasis on the Cheloniidae.
Detailed descriptions of the development of Dermochelys coriacea were presented
by Renous et al. (1989).
Although studies on marine turtles have contributed to the understanding of the
development of the genital system in reptiles, no review has specifically addressed
the ontogeny of marine turtle gonads. This chapter traces the ontogeny (morphology)
of the gonads and associated ducts of marine turtles from embryogenesis through
puberty to the adult, including changes linked with the reproductive cycle; lesser
emphasis is placed on the development of the copulatory organs. The primary
information is derived from studies on marine turtles; secondary support is obtained
from studies on other turtles and, in turn, other reptiles. The approach focuses on
marine turtles as much as possible rather than addressing the topic of gonadal
ontogeny of reptiles (see Fox, 1977; Raynaud and Pieau, 1985). It should be remembered that morphological change, whether it be associated with development, growth,
maturation, or reproduction, should not be viewed in isolation; the ontogenetic
changes are driven by a complex suite of genetically coded interactive endocrine
changes that occur in the context of endogenous and exogenous events throughout
the life of the turtle (Owens, 1997).
7.2 EMBRYOGENESIS
During ovulation, multiple unfertilized ova are expelled from the ovary into the body
cavity, from which they pass into the infundibulum of the oviduct; multiple ovulations for the entire clutch occur over a short time interval (Aitken et al., 1976; Owens,
1980). Fertilization occurs in the anterior of the oviduct (infundibulum or aglandular
zone) before each ovum is surrounded by albumen (Miller, 1985). Cleavage and the
formation of the gastrula occur as each ovum passes down the oviduct (Miller, 1985).
Sequentially during this passage, each ovum is surrounded by albumen, the shell
1123 book.book Page 200 Monday, November 11, 2002 11:11 AM