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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
The gonads are arranged hanging from four radial canals so that when viewed from above, the gonads are lined perpendicularly. The manubrium , colored tan, hangs down in the middle. The bell of the jellyfish (medusae) is only 1–3 cm (0.4–1.2 in) in diameter, [ 2 ] exceptionally up to 4 cm (1.6 in), and when fully extended a tentacle can be ...
Male gonad (testes, left) and female gonad (ovaries, right) Males have two testicles of similar size contained within the scrotum, which is an extension of the abdominal wall. [1] Scrotal asymmetry, in which one testicle extends farther down into the scrotum than the other, is common. This is because of the differences in the vasculature's ...
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 ...
Free-living males and unparasitized females in these species never have fully developed gonads. Thus, males never mature without attaching to a female, and die if they cannot find one. [4] At birth, male ceratioids are already equipped with extremely well-developed olfactory organs that detect scents in the water. Males of some species also ...
The stout infantfish is the smallest and lightest adult fish and is in fact the smallest vertebrate in the world; the females measures 8.4 mm (0.33 in) and the male just 7 mm (0.28 in). [ 35 ] A rare giant oarfish ( Regalecus glesne ), 7-metre (23 ft) long, captured in 1996
The male portion of the reproductive tract includes both a short posterior vas deferens and a longer anterior vas deferens. The posterior vas deferens is followed by the prostate, and the anterior vas deferens flows through the haemocoele , an enlarged blastula filled with blood, of the head and opens into a muscular penis which is engulfed in ...