Thickset, blunt-snouted toothed whale (Physeter catodon, family Physeteridae) with small, paddlelike flippers and rounded humps on the back. Sperm whales have an enormous head, squarish in profile, and a narrow, underslung lower jaw with large conical teeth that fit into sockets in the toothless upper jaw when the mouth is closed. They are dark blue-gray or brownish. (Herman Melville's Moby-Dick was presumably an albino.) The male grows to 60 ft (18 m). Herds of 15–20 live in temperate and tropical waters worldwide. They commonly dive to 1,200 ft (350 m), feeding primarily on cephalopods. The whales have been hunted for their spermaceti (a waxy substance in the snout, used in ointments and cosmetics) and for ambergris. The pygmy sperm whale (genus Kogia) is a black dolphinlike whale, about 13 ft (4 m) long, of the Northern Hemisphere that lacks commercial value.
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Male reproductive cell. In mammals, sperm are produced in the testes and travel through the reproductive system. At fertilization, one sperm of the roughly 300 million in an average ejaculation (see semen) fertilizes an egg (see ovary) to produce an offspring. At puberty, immature cells (spermatogonia) begin a maturation process (spermatogenesis). A mature human sperm has a flat, almond-shaped head, with a cap (acrosome) containing chemicals that help it penetrate an ovum. It is essentially a cell nucleus, with 23 chromosomes (including either the X or Y that determines the child's sex). A flagellum propels the sperm, which may live in a woman's reproductive tract for two to three days after sexual intercourse, to the egg. Sperm may be frozen and stored for artificial insemination.
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Motile sperm cells typically move via flagella and require water in order to swim toward the egg for fertilization. The uniflagellated sperm cells (with one flagellum) produced in most animals are referred to as spermatozoa, and are known to vary in size.
Motile sperm are also produced by many protists and the gametophytes of bryophytes, ferns and some gymnosperms such as cycads and ginkgo. The sperm cells are the only flagellated cells in the life cycle of these plants. In many ferns and lycophytes, they are multi-flagellated (carrying more than one flagellum).
In order to move towards the ova the sperm swim through the womans vaginal juices coating the walls of the womb and cervix.
Because spermatia cannot swim,they depend on their environment to carry them to the egg cell. Some red algae, such as Polysiphonia, produce non-motile spermatia that are spread by water currents after their release. The spermatia of rust fungi are covered with a sticky substance. They are produced in flask-shaped structures containing nectar, which attract flies that transfer the spermatia to nearby hyphae for fertilization in a mechanism similar to insect pollination in flowering plants.
Fungal spermatia (also called pycnidiospores) may be confused with conidia. Conidia are spores that germinate independently of fertilization, whereas spermatia are gametes that are required for fertilization. In some fungi, such as Neurospora crassa, spermatia are identical with microconidia as they can perform both functions of fertilization as well as giving rise to new organisms without fertilization.
In some protists, fertilization also involves sperm nuclei, rather than cells, migrating toward the egg cell through a fertilization tube. Oomycetes form sperm nuclei in a syncytical antheridium surrounding the egg cells. The sperm nuclei reach the eggs through fertilization tubes, similar to the pollen tube mechanism in plants.
Sperm traits in Chinook salmon depend upon activation medium: implications for studies of sperm competition in fishes.
Oct 01, 2009; Introduction In salmonids, and most other externally fertilizing fishes, the period during which spawned ova can be fertilized is...