An ovariole is a tubular component of the insect ovary, and the basic unit of egg production. Each ovariole is composed of a germarium (the

germline In biology and genetics, the germline is the population of a multicellular organism's cells that pass on their genetic material to the progeny (offspring). In other words, they are the cells that form the egg, sperm and the fertilised egg. They ...

stem cell niche) at the anterior tip, a set of developing

oocytes An oocyte (, ), oöcyte, or ovocyte is a female gametocyte or germ cell involved in reproduction. In other words, it is an immature ovum, or egg cell. An oocyte is produced in a female fetus in the ovary during female gametogenesis. The female ge ...

contained within follicles, and a posterior connection to a common oviduct. While most insects have two ovaries, the number of ovarioles within each ovary varies across insect species. This number may also be variable across individuals within a species, or between the left and right ovaries within an individual.

Types

Ovarioles are often classified into one of several types by the presence and position of nurse cells. These specialized cells provide nutrition and molecules important for embryonic patterning to the developing oocyte. Ovarioles that lack nurse cells are referred to as ''panoistic'' and ovarioles with nurse cells are referred to as ''meroistic''. Meroistic ovarioles are further classified according to where nurse cells are located. In ''polytrophic meroistic'' ovarioles, nurse cells are adjacent to the developing oocyte. In ''telotrophic meroistic'' ovarioles, nurse cells are located in the germarium and connect to developing ooctypes via nutritive cords.

In ''Drosophila melanogaster''

In the fruit fly ''

Drosophila melanogaster ''Drosophila melanogaster'' is a species of fly (the taxonomic order Diptera) in the family Drosophilidae. The species is often referred to as the fruit fly or lesser fruit fly, or less commonly the "vinegar fly" or "pomace fly". Starting with Ch ...

'', a common

model organism A model organism (often shortened to model) is a non-human species that is extensively studied to understand particular biological phenomena, with the expectation that discoveries made in the model organism will provide insight into the workin ...

for developmental research, each ovary typically contains between 16 and 20 polytrophic meroistic ovarioles. These ovarioles continuously produce eggs through division and differentiation of the germline stem cells, located in the anterior tip of the germarium. There are also several populations of somatic support cells in the germarium, including terminal filament cells, cap cells, and anterior escort cells. The process of oogenesis within the Drosophila ovariole has been divided into 14 identifiable stages. Developing oocytes are arranged within the ovariole in an

ontogenic Ontogeny (also ontogenesis) is the origination and development of an organism (both physical and psychological, e.g., moral development), usually from the time of fertilization of the egg to adult. The term can also be used to refer to the stu ...

series, with early stage oocytes toward the anterior and later stage oocytes posterior. At the end of stage 14, the egg passes through the lateral oviduct before entering the common oviduct and then exiting via the uterus.

References

Insect anatomy {{insect-anatomy-stub