A<unk>  is a medical tool for investigating body cavities, with a form dependent on the body cavity for which it is designed.  In old texts, the<unk>  may also be referred to as a diopter or dioptra.
Vaginal specula were used by the Romans, and<unk>  artifacts have been found in Pompeii. A vaginal<unk> , developed by J. Marion Sims, consists of a hollow cylinder with a rounded end that is divided into two hinged parts, somewhat like the beak of a duck. The<unk>  is inserted into the vagina to dilate it for examination of the vagina and cervix.
A specialized  form of vaginal<unk>  is the weighted<unk> , which consists of a broad half tube which is bent at about a 90 degree angle, with the channel of the tube on the exterior side of the angle.  One end of the tube has a roughly spherical metal weight surrounding the channel of the<unk> .  A weighted<unk>  is placed in the vagina during vaginal surgery with the patient in the lithotomy position.  The weight holds the<unk>  in place and frees the surgeon's hands for other tasks.
Vaginal specula are also used for anal surgery, although several other forms of anal specula exist. One common form, the sigmoidoscope, resembles a tube that has a removable bullet shaped insert. When the<unk>  is inserted into the rectum, the insert dilates the rectum to the diameter of the tube. The insert is then removed, leaving the tube to allow examination of the rectum.  This style of anal<unk>  is one of the oldest designs for surgical instruments still in use, with examples dating back many centuries.
Ear specula resemble a funnel, and come in a variety of sizes.
Nasal specula have two relatively flat blades with handle.  The instrument is hinged so that when the handles are squeezed together the blades spread laterally, allowing examination.
All specula were formerly made of metal, and sterilized after use. However, many, especially those used in Emergency Departments and Doctor's offices, are now made of plastic, and are sterile, disposable, single-use items.  Those used in surgical suites are still commonly made of metal.
Vaginal and anal specula are also sometimes used as sex toys.
Contrary to some previously-held opinions, the<unk>  does not cause damage to the vaginal opening, as many gynecological teachers will attest.  In very few states in the United States, vaginal specula are illegal for personal use, but since there was a popular cervical self-examination component to the second-wave feminist movement, many states are either much more lenient or have completely relinquished restrictions on<unk>  use.  However, distributors still face specific guidelines about which specula may or may not be sold.
Speculum
Dermatophyte
Ovum
Biofilm
Exudate
Aqueous humour
Nucleosol
Algae