Gill slit

Gill slits are individual openings to gills, i.e., multiple gill arches, which lack a single outer cover. Such gills are characteristic of cartilaginous fish such as sharks, and rays. Most of these have five pairs, but a few species have 6 or 7 pairs. Shark gill slits are not covered, but lie in a row behind the head. The anterior edge of a gill slit is motile, moving outward to allow water to exit, but closing to prevent reverse flow. This modified slit, called a spiracle, lies just behind the eye, which assists the shark with taking in water during respiration and plays a major role in bottom–dwelling sharks. Spiracles are reduced or missing in active pelagic sharks. While the shark is moving, water passes through the mouth and over the gills in a process known as "ram ventilation". While at rest, most sharks pump water over their gills to ensure a constant supply of oxygenated water. A small number of species have lost the ability to pump water through their gills and must swim without rest. These species are obligate ram ventilators and would presumably asphyxiate if unable to move. Obligate ram ventilation is also true of some pelagic bony fish species. In contrast, bony fishes have a single outer bony gill covering called an operculum.

Gill

A gill (ⁱ/ɡɪl/) is a respiratory organ found in many aquatic organisms that extracts dissolved oxygen from water and excretes carbon dioxide. The gills of some species, such as hermit crabs, have adapted to allow respiration on land provided they are kept moist. The microscopic structure of a gill presents a large surface area to the external environment.

Many microscopic aquatic animals, and some larger but inactive ones, can absorb adequate oxygen through the entire surface of their bodies, and so can respire adequately without a gill. However, more complex or more active aquatic organisms usually require a gill or gills.

Gills usually consist of thin filaments of tissue, branches, or slender, tufted processes that have a highly folded surface to increase surface area. A high surface area is crucial to the gas exchange of aquatic organisms, as water contains only a small fraction of the dissolved oxygen that air does. A cubic meter of air contains about 250 grams of oxygen at STP. The concentration of oxygen in water is lower than air and it diffuses more slowly. In fresh water, the dissolved oxygen content is approximately 8 cm³/L compared to that of air which is 210 cm³/L. Water is 777 times more dense than air and is 100 times more viscous. Oxygen has a diffusion rate in air 10,000 times greater than in water. The use of sac-like lungs to remove oxygen from water would not be efficient enough to sustain life. Rather than using lungs, "[g]asesous exchange takes place across the surface of highly vascularised gills over which a one-way current of water is kept flowing by a specialised pumping mechanism. The density of the water prevents the gills from collapsing and lying on top of each other, which is what happens when a fish is taken out of water."

Gill, Massachusetts

Gill is a town in Franklin County, Massachusetts, United States. The population was 1,500 at the 2010 census. It is part of the Springfield, Massachusetts Metropolitan Statistical Area. The campus of Northfield Mount Hermon School is located in the Mount Hermon section of the town.

History

Prior to the arrival of English colonists, the Massachusetts portion of the Connecticut River valley was occupied by the Nipmuc, an Algonquin-speaking tribe. A site on the river near the great falls shows evidence of human habitation dating back 10,000 years or more. In the 1670s the Nipmuc had a village called Peskeompscut in that area. During King Philip's War in 1676, Captain William Turner led 150 colonists in an attack on this settlement, in which several hundred Indians (mostly women, children, and elderly) were slain. The falls came to be known as Turners Falls after Turner, who was slain in the battle. (The falls thereafter gave that name to the village of Turners Falls in neighboring Montague.)

Gill (name)

Gill may be a surname or given name, derived from a number of unrelated sources;

People with the surname Gill