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Most male fish have two testes of similar size. In the case of sharks, the testes on the right side is usually larger [citation needed].The primitive jawless fish have only a single testis, located in the midline of the body, although even this forms from the fusion of paired structures in the embryo.
A gonad, sex gland, or reproductive gland [1] is a mixed gland and sex organ that produces the gametes and sex hormones of an organism. Female reproductive cells are egg cells, and male reproductive cells are sperm. [2] The male gonad, the testicle, produces sperm in the form of spermatozoa. The female gonad, the ovary, produces egg cells
Fish Gonads: CASI has also been observed in fish species where gonadal cells retain their sex identity independent of external hormonal cues. [ 39 ] [ 40 ] [ 41 ] The mechanisms underlying CASI highlight the diversity and complexity of sex determination processes across species.
In embryology, the genital ridge (genital fold or gonadal ridge) is the developmental precursor to the gonads. The genital ridge initially consists mainly of mesenchyme and cells of underlying mesonephric origin. Once oogonia [clarification needed] enter this area they attempt to associate
Most normal female fish have two ovaries. In some elasmobranchs, only the right ovary develops fully. In the primitive jawless fish and some teleosts, there is only one ovary, formed by the fusion of the paired organs in the embryo. [57] Fish ovaries may be of three types: gymnovarian, secondary gymnovarian or cystovarian.
Germ cells migrate from near the allantois and colonize the primordial gonads. In the female, the germ cells colonise the cortex and become oogonia. In the male, the germ cells colonise the seminiferous cords of the medulla, becoming spermatogonia.
Fish embryos go through a process called mid-blastula transition which is observed around the tenth cell division in some fish species. Once zygotic gene transcription starts, slow cell division begins and cell movements are observable. [4] During this time three cell populations become distinguished. The first population is the yolk syncytial ...
2 and 5 sex cords A depiction of the migration of the cells which will give rise to the sex cords into the genital ridge where they will become the gonads of the embryo. Sex cords are embryonic structures which eventually will give rise (differentiate) to the adult gonads (reproductive organs). [1]