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The egg is found in the faeces, sputum, or urine of the definitive host. Depending on the species, it will either be non-embryonated (immature) or embryonated (ready to hatch). The eggs of all trematodes (except schistosomes) are operculated. Some eggs are eaten by the intermediate host (snail) or they are hatched in their habitat (water).
The trematode Hirudinella ventricosa releases eggs in strings. Each egg contains a single miracidium, while the string contains living spermatozoa. Miracidia have cilia that are only present in the upper portion of the body near an apical gland with 12 hook-like spines in the opening. [2]
Usually there is a single ovary with an oviduct, a seminal receptacle, a pair of vitelline glands (involved in yolk and egg-shell production) with ducts, the ootype (a chamber where eggs are formed), a complex collection of glands cells called Mehlis’ gland, which is believed to lubricate the uterus for egg passage.
The eggs, which are oval, operculated, and light brown, are released from adult Alaria and excreted from the final host's faeces and hatched into miracidium that infect the snail host, in which the eggs then give rise to the asexual stage known as sporocysts. The sporocysts then produce cercariae.
The egg is about 70–85 μm long by 44 μm wide, and the early stages of cleavage contain between 16 and 32 cells. The adult female is 18–30 millimetres ( 3 ⁄ 4 – 1 + 1 ⁄ 8 in) long and is easily recognized by its trademark "barber pole" coloration.
Egg of S. haematobium. Note the pointed spine on the left tip. Normal infection of adults does not produce symptoms. When eggs are released, they sometimes become permanently stuck in the bladder and cause pathological symptoms. The eggs are initially deposited in the muscularis propria which leads to
The eggs from pasture-raised chickens have less cholesterol and more nutrients, Steele said, because of their healthier, more varied diets. Yolks are not the only thing that come in different colors.
Mature egg cells are produced by mitotic divisions, and these cells directly develop into embryos. In flowering plants, cells of the gametophyte can undergo this process. The offspring produced by apomictic parthenogenesis are full clones of their mother, as in aphids. [23] Parthenogenesis involving meiosis is more complicated.