from The American Heritage® Dictionary of the English Language, 4th Edition
- n. Botany A nutritive tissue within the sporangium, particularly within an anther.
- n. Anatomy A membranous layer or region, especially the iridescent membrane of the choroid of certain mammals.
- n. Anatomy A layer of fibers of the corpus callosum forming the roof of part of the lateral ventricle of the brain.
from Wiktionary, Creative Commons Attribution/Share-Alike License
- n. A membranous layer of tissue
from the GNU version of the Collaborative International Dictionary of English
- n. An area in the pigmented layer of the choroid coat of the eye in many animals, which has an iridescent or metallic luster and helps to make the eye visible in the dark. Sometimes applied to the whole layer of pigmented epithelium of the choroid.
from The Century Dictionary and Cyclopedia
- n. In botany, the cell or layer of cells which is immediately outside an archesporium. It is disorganized and absorbed as the spores develop and mature. Also tapete.
- n. The pigmentary layer of the retina; the tapetum nigrum.
- n. The fibers from the corpus callosum forming a layer lining the roof of the middle and posterior cornua of the lateral ventricles.
All night-prowling animals have widely dilatable pupils, and in addition to this they have in the retina a special organ called the tapetum lucidum, the function of which is to reflect to a focus in front of them the relatively few rays of light that enter the widely-dilated pupil and thus enable them the better to see their way.
It's the crystals inside their retina, inside a layer called tapetum.
The tapetum is a thick reflective membrane, 15 cells wide, directly beneath the retina.
The green glow of the ratfish eye is due to a lowlight adaptation called a tapetum lucidum,
no tapetum: The tapetum is a layer of the eye that reflects light.
The effect you are referring to is called eyeshine yet the phenomenon behind it is caused by light amplification within the eye of an organism with a tapetum lucidium layer.
» A cat sees about six times better than a human at night because of the tapetum lucidum, a layer of extra reflecting cells which absorb light.
This tapetum lucidum, in Latin “carpet of light,” accounts for all the photographs you have of your dog with brilliant light shining out where their eyes should be.
When animal eyes glow at night when light hits them, it is the tapetum you're seeing.
Tarsiers lack a tapetum even though they are nocturnal which suggests that tarsiers may have once been diurnal and became nocturnal in response to some change in their ecology, for example, the addition of new predators or competitors.