External gills usually contains muscle tissue, and may be moved by the animal as a free appendage, in order to stir up stagnant water. The stalk is lined by many thinly walled filaments (fimbriae), containing the majority of blood vessels used in gas exchange. Animals usually have one external gill originating on each gill arch (except the hyoid), which leads to there being three pairs of external gills in salamanders, and four in the gilled larvae of lungfish. External gills External gills are the gills of an animal, most typically an amphibian, that are exposed to the environment, rather than set inside
Pint pint can still be the principal unit used, otherwise metric units (usually the non-SI litre) must be used. There is no requirement for the litre quantity to be round numbers: thus the quantity of milk sold in a non-returnable container may be 1 pint, but will have "568 ml 1 pint", or just "568 ml" on the label. Many recipes published in the UK and Ireland still give ingredient quantities in imperial, where the pint is often used as a unit for larger liquid quantities. The Guild of Food Writers recommends that new recipes be published in metric units. The